---
title: Retention Glossary: Cohorts, Day N and Three Types
description: Plain definitions of retention terms: install cohort, Day 0, Day N, classic, rolling and cumulative retention, bounded numbers, diagonals and mix shift.
url: https://retentioncohorts.com/glossary/
---

[Home](https://retentioncohorts.com/) / Glossary

# Retention glossary

Plain definitions for the terms used on this site.

**Short answer**

The words you need to read a cohort retention table: cohorts, Day 0 and Day N, the three retention types, bounded and unbounded numbers, diagonals, mix shifts and more, each in one or two plain sentences.

## What do the retention terms mean?

**Install cohort:** A group of users who installed on the same day (or week). The unit every retention number is about.

**Day 0:** The install day. Activity on Day 0 never counts as a return.

**Day N:** The Nth day after install, counted in calendar days in one time zone or in 24-hour windows; say which.

**Return event:** What counts as being active: usually any app open. Some teams use a meaningful action instead.

**Classic retention:** The share of a cohort active on exactly Day N. Also called N-day, Day-N or exact-day retention. Bounded.

**N-day retention:** Another name for classic retention.

**Rolling retention:** The share of a cohort active on Day N or any later observed day. Also called unbounded retention. Keeps rising as time passes.

**Unbounded retention:** Another name for rolling retention, after its open-ended window.

**Cumulative retention:** The share of a cohort active at least once between Day 1 and Day N. Bounded, never falls as N grows.

**Bracket retention:** The share of a cohort active at least once inside a range of days, such as Days 8 to 14. Cumulative is a bracket that always starts at Day 1.

**Bounded:** A retention number that is fixed once its window has passed. Classic and cumulative are bounded; rolling is not.

**Mature cell:** A cell whose Day N has fully passed for that cohort. Only mature cells should be compared.

**As-of date:** The last day included in the data. Rolling numbers only mean something next to it.

**Cohort table:** Install cohorts as rows, days since install as columns, retention in the cells. Usually a triangle, because newer cohorts have fewer days.

**Diagonal:** Cells in a cohort table that share one calendar date. A bright or dark diagonal points to an event on that day.

**Retention curve:** One cohort's (or a pooled set's) retention plotted against Day N.

**Flattening point:** Where a classic retention curve stops falling and levels off at its habitual users.

**Blended retention:** Retention across all channels together. Moves when the channel mix moves, even if no channel changed.

**Mix shift (Simpson's paradox):** A blended number moving the opposite way to, or without, its parts because the share of each part changed.

**Churn rate:** The share of users who stop using the app over a period. Roughly the flip side of retention, but defined in many ways; check which.

**Stickiness (DAU/MAU):** Daily active users divided by monthly active users: how often active users come back. A complement to cohort retention, not a replacement.

See this on your own app

The Linkrunner glossary defines these and other mobile measurement terms, from cohort analysis to attribution windows.

- [Linkrunner glossary](https://linkrunner.io/glossary?utm_source=retentioncohorts&utm_medium=referral&utm_campaign=glossary&utm_content=panel)
- [Cohort analysis in the Linkrunner glossary](https://linkrunner.io/glossary/what-is-cohort-analysis?utm_source=retentioncohorts&utm_medium=referral&utm_campaign=glossary&utm_content=panel)
- [Create a free account (25k installs free)](https://dashboard.linkrunner.io/sign-in?utm_source=retentioncohorts&utm_medium=referral&utm_campaign=glossary&utm_content=panel)