Glossary44
Every term in the book, defined once, linked to where it's taught.
A
ActivationThe moment a new user first experiences the product's core value — the gate between signup and retention. lesson 04 Aha MomentThe specific action-threshold that predicts long-term retention (e.g. '7 friends in 10 days'). lesson 04 AnchoringThe bias where the first number seen becomes the reference point every later price is judged against. lesson 11 Atomic NetworkThe smallest self-sustaining network a product needs before it works at all — one campus, one team, one city block. lesson 02 C
ChurnThe rate at which users or revenue stop returning in a period. The silent tax on all acquisition. lesson 10 Cohort AnalysisTracking groups of users who started together, so time-based decay isn't hidden by new-user growth. lesson 10 Cold-Start ProblemThe chicken-and-egg failure mode of network products: no value until there are users, no users until there's value. lesson 02 Cycle TimeHow long one full viral loop takes. Halving cycle time compounds faster than doubling K. lesson 05 D
Decoy EffectAdding an intentionally inferior option to make a target option look like the obvious choice. lesson 11 DunningThe recovery flow for failed subscription payments — retries, emails, grace periods. lesson 11 E
Endowment EffectPeople value what they already own more than the identical thing they don't. Fuel for streaks and stored value. lesson 03 F
Feed RankingOrdering content by predicted engagement instead of recency, learned from behavioral signals. lesson 09 Freemium BoundaryThe line between what's free and what's paid. Drawn right, free sells; drawn wrong, free satisfies. lesson 11 G
Growth AccountingDecomposing top-line growth into new + resurrected − churned, so 'flat' can be diagnosed. lesson 13 Growth LoopA closed cycle where the output of one user's action becomes the input acquiring the next user. lesson 05 Growth-Team OperationsHow growth teams organize and run: North-Star metrics, experiment velocity, and the cadence that compounds wins. lesson 14 H
Hook ModelNir Eyal's four-phase habit loop: trigger → action → variable reward → investment. lesson 03 I
ICE ScoreImpact × Confidence × Ease — a fast, imperfect triage for ranking experiment ideas. lesson 14 Interrupt BudgetThe finite tolerance a user has for notifications before they mute or delete. Spend it like money. lesson 07 Investment PhaseThe Hook Model step where users put something in — data, content, reputation — that loads the next trigger. lesson 03 K
K-FactorAverage invites sent × conversion rate per invite. Above 1.0, growth is self-sustaining. lesson 05 L
Latent DemandA want that exists before the product that satisfies it — visible in workarounds, not surveys. lesson 01 Loss AversionLosses hurt roughly twice as much as equivalent gains feel good. The engine behind streaks. lesson 03 N
Natural FrequencyHow often the underlying job-to-be-done actually occurs — the ceiling on any habit ambition. lesson 10 Network DensityThe share of possible connections that exist among a user's relevant graph. Density predicts retention. lesson 02 Network EffectEach additional user makes the product more valuable for existing users. lesson 02 North-Star MetricThe single metric that best proxies delivered customer value, decomposed into movable inputs. lesson 14 Notification EngineeringDesigning what, when, and how often to notify so attention is earned rather than spent — governed by the interrupt budget. lesson 07 P
PeekingChecking an experiment early and stopping when it looks good — a reliable way to ship noise. lesson 13 Pricing PsychologyHow framing and cognitive bias — anchoring, decoys, loss aversion — shape what people will actually pay. lesson 11 Q
Quick Ratio(New + resurrected) ÷ churned. Above 1 you grow; growth accounting in one number. lesson 13 R
ResurrectionBringing a dormant user back to active use; often cheaper than acquiring a stranger. lesson 10 Retention CurvePercent of a cohort still active over time. Flattening curves mean product-market fit; decaying ones don't. lesson 10 Reward ScheduleThe timing pattern of rewards. Variable-ratio schedules produce the most persistent behavior. lesson 03 S
Social ProofPeople infer correct behavior from others' behavior — follower counts, 'X friends use this'. lesson 03 Stopping CueAny signal that a session could end — page bottoms, episode credits. Removed by infinite scroll and autoplay. lesson 06 Stored ValueAccumulated data, content, or reputation that makes a product better with use and costly to leave. lesson 03 StreakA visible run of consecutive-day usage that converts loss aversion into daily attendance. lesson 08 V
Variable RewardA reward whose size or presence is unpredictable — the 'maybe' that keeps the pull-to-refresh pulling. lesson 03 Viral LoopExposure → conversion → re-exposure: the repeating chain by which users create users. lesson 05 ViralityThe tendency of a product to spread through its own users — each user's activity helping create the next. lesson 05 W
WedgeThe deliberately narrow first market a product dominates before expanding outward. lesson 01 Willingness to PayThe maximum a segment will actually part with — measured by behavior, not by asking. lesson 11 Win-BackA targeted campaign or flow aimed at resurrecting churned users, often with a second first-impression. lesson 10