Glossary // A to Z / Short, exact definitions

Marketing glossaryEvery term in one sentence first.

Plain-language definitions of digital marketing terms, from A/B tests to zero-click search. Each entry starts with a one-sentence definition and links to a related tool or article.

Showing 64 of 64 terms

A

A/B test: An A/B test compares two versions of a page, ad or message by showing each to a random share of visitors and measuring a chosen result.
Account-based marketing (ABM): Account-based marketing focuses marketing and sales effort on a defined list of target companies, with messages tailored to each account's situation.
Ad frequency: Ad frequency is the average number of times a person sees an ad in a period.
Adstock: Adstock is the carryover effect of advertising, where spend in one period keeps influencing results in later periods while fading at a steady rate.
Answer engine optimization (AEO): Answer engine optimization prepares content to be used as a direct answer in featured snippets, voice assistants and AI summaries.
Attribution: Attribution assigns credit for a conversion to the marketing touchpoints that contributed to it.
Average revenue per account (ARPA): Average revenue per account is the typical revenue a customer account generates in a period, calculated by dividing total revenue by the number of accounts.

B

Bass diffusion model: The Bass diffusion model describes how a new product is adopted over time, using an innovation rate for early adopters and an imitation rate for people influenced by others.
Break-even ROAS: Break-even ROAS is the lowest return on ad spend at which a campaign covers product costs and ad spend.

C

CAC payback period: CAC payback period is the number of months of gross profit needed to recover the cost of winning a customer.
Carryover rate (θ): The carryover rate, written θ, is the share of one period's advertising effect that persists into the next.
Churn rate: Churn rate is the share of customers who stop buying or cancel in a given period.
Click-through rate (CTR): Click-through rate is the percentage of people who see an ad and click it, calculated as clicks divided by impressions times 100.
Cohort: A cohort is a group of customers who share a starting point, such as the month they signed up.
Conversion funnel: A conversion funnel maps the stages a prospect passes through, from first visit to purchase, with the share that continues at each stage.
Conversion rate: Conversion rate is the share of visitors who complete a goal, such as buying or submitting a form.
Cost per acquisition (CPA): Cost per acquisition is the advertising spend needed to earn one conversion, such as a lead or purchase.
Cost per click (CPC): Cost per click is the average price paid for one click on an ad, calculated as spend divided by clicks.
Cost per mille (CPM): Cost per mille is the price paid for one thousand ad impressions, calculated as spend divided by impressions times 1,000.
Customer acquisition cost (CAC): Customer acquisition cost is the total sales and marketing spend needed to win one new customer.
Customer lifetime value (LTV): Customer lifetime value estimates the gross profit a customer generates over the whole relationship.
Customer retention: Customer retention is the share of customers who continue to buy or subscribe over time.

D

Demand generation: Demand generation is the set of marketing activities that build awareness and interest in a category and brand, so that buyers reach out or respond later.
Diminishing returns: Diminishing returns describe how each additional unit of input, such as an ad dollar, yields less extra output than the one before.

E

E-E-A-T: E-E-A-T stands for experience, expertise, authoritativeness and trustworthiness, the qualities Google's quality guidelines ask raters to look for in content.
Entity: An entity is a clearly defined thing that search and AI systems can recognize and connect, such as a company, person, product or place.
Erlang C: Erlang C is a queueing formula from telecom engineering that estimates how many agents are needed so that a chosen share of arrivals is served within a target wait.

F

Featured snippet: A featured snippet is a highlighted answer that Google shows at the top of some search results, taken from a page and displayed as a paragraph, list or table.
Flesch reading ease: Flesch reading ease is a score based on average sentence length and average syllables per word.
Forgetting curve: The forgetting curve, described by Hermann Ebbinghaus, shows how memory of information declines over time without reinforcement, following roughly exponential decay.

G

Generative engine optimization (GEO): Generative engine optimization is the practice of improving how often AI engines such as ChatGPT, Perplexity and Copilot mention or cite a brand in their generated answers.
Gross margin: Gross margin is the share of revenue left after the direct costs of making and delivering a sale, calculated as revenue minus direct cost, divided by revenue.

H

Half-life: Half-life is the time it takes for an effect to fall to half its starting size.
Hill function: The Hill function is an S-shaped or saturating curve from biochemistry that relates a dose to a response.

I

Impression: An impression is one instance of an ad being displayed to a user.
Incrementality: Incrementality is the extra result caused by marketing that would not have happened otherwise.

K

K-factor: The K-factor is the number of new users each existing user brings in, calculated as invites sent per user times the conversion rate of those invites.

L

Large language model (LLM): A large language model is a neural network trained on very large amounts of text to predict and generate language.
Last-click attribution: Last-click attribution gives all credit for a conversion to the final touchpoint before it.
Little's Law: Little's Law states that the average number of items in a system equals the arrival rate times the average time each item spends there.
llms.txt: The llms.txt file is a proposed convention that places a curated, plain-text map of a site's key pages at the root domain for AI systems to read.
Lookalike audience: A lookalike audience is a group of people chosen by an ad platform because they resemble an existing set of customers.

M

Marginal ROAS: Marginal ROAS is the revenue earned from the next dollar of ad spend, as opposed to the average across all spend.
Marketing qualified lead (MQL): A marketing qualified lead is a contact whose behavior and profile suggest buying interest, based on rules such as downloads, visits or company size.
Markup: Markup is profit expressed as a percentage of cost, calculated as price minus cost, divided by cost.
Media mix modeling: Media mix modeling uses historical spend and sales data to estimate how much each channel contributes, including carryover and saturation effects.
Multi-touch attribution: Multi-touch attribution spreads credit for a conversion across several touchpoints, using rules such as linear, time decay or position based.

O

Organic traffic: Organic traffic is the set of visits that arrive from unpaid search results and other non-advertising sources.

P

P-value: A p-value is the probability of seeing a result at least as extreme as the one observed if there were no real effect.

R

Referral loop: A referral loop is a growth system in which existing customers bring in new ones, who then refer further customers.
Retargeting: Retargeting shows ads to people who already visited a site or interacted with a brand.
Return on ad spend (ROAS): Return on ad spend is the revenue earned for each dollar spent on advertising, calculated as revenue divided by ad spend.
Return on investment (ROI): Return on investment measures the profit from an investment relative to its cost, calculated as net gain divided by cost.

S

Sales development representative (SDR): A sales development representative is a salesperson who responds to inbound leads and starts outbound conversations, then passes qualified opportunities to account executives.
Sales qualified lead (SQL): A sales qualified lead is a contact that the sales team has reviewed and accepted as a real opportunity, typically after confirming need, budget, authority and timing.
Saturation: Saturation is the point at which additional advertising spend produces little extra response because the most responsive audience has already been reached.
Schema markup: Schema markup is structured data, usually written in JSON-LD, that labels the meaning of page content using the shared schema.org vocabulary.
Search engine optimization (SEO): Search engine optimization is the work of earning higher, more visible placement in search results through technical health, relevant content and credible links.
Share of voice: Share of voice is a brand's portion of total advertising spend or visibility in its category.
SIR model: The SIR model is an epidemiology framework that divides a population into susceptible, infected and recovered groups.
Statistical power: Statistical power is the chance that a test detects a real effect of a given size.

V

Viral coefficient: The viral coefficient is another name for the K-factor: the average number of new users generated by each user through invites or sharing.

W

Weber-Fechner law: The Weber-Fechner law says that the smallest noticeable change in a stimulus is proportional to its starting size.

Z

Zero-click search: A zero-click search is one where the user gets an answer on the results page and does not visit any website.