Glossary

Calorie Deficit

A state where you consume fewer calories than your body burns over a defined period. The mechanism through which weight loss is hypothesized to occur. Often misapplied in consumer apps.

RMR vs BMR

Two related-but-different measures of how many calories your body burns at rest. RMR (resting metabolic rate) is what most consumer apps actually estimate; BMR (basal metabolic rate) is the more clinical version requiring overnight fasting and specific lab conditions.

Ecosystem Lock-In

The pattern where a product becomes hard to switch away from because your data, integrations, and habits are entangled with a specific platform or vendor. The dominant strategic move in consumer-app design over the last decade.

Food Database

The catalog of foods and their nutrition information that a calorie-tracking app uses to look up entries. Database size, verification quality, and update cadence are the dominant inputs into a tracker's accuracy.

HRV (Heart-Rate Variability)

The variation in time between successive heartbeats, used by smart rings, smartwatches, and chest straps as a peripheral signal correlated with autonomic nervous system state and sleep stages.

MAPE (Mean Absolute Percentage Error)

A measurement-accuracy metric used to evaluate calorie-tracking apps, sleep trackers, and other consumer-grade measurement devices against a reference standard.

Freemium

A pricing model where a basic version of a product is free and a 'premium' version requires a subscription. Common in calorie-tracking, meditation, and productivity apps; structurally aligns the vendor with the goal of converting free users to paid.

Latency

The time delay between a user action and the system's response. The dominant felt-quality metric for consumer apps; affects everything from autocomplete to AI chat to smart-lock unlock time.

Machine Learning (ML)

The broad category of statistical algorithms that learn patterns from data instead of being explicitly programmed. The technology underneath consumer-grade AI features — sleep staging, photo recognition, text generation — and the source of both their gains and their failures.

Photo Recognition (AI Food Vision)

The machine-learning capability that identifies foods, portion sizes, and nutrition values from a photograph of a meal. The technology underneath the photo-first calorie-tracking category.

PWA (Progressive Web App)

A web application that can be installed to a phone home screen and run with native-app-like behavior — a category that affects which apps you actually need to install from an app store.

Sleep Stages

The four stages your sleep cycles through (N1, N2, N3, REM) — the underlying biology that consumer sleep trackers attempt to estimate from peripheral signals like heart rate and HRV.