glossary
Six terms that come up across the answers. Each definition is what we mean when we use the word here — not a generic dictionary entry.
Barcode
EAN-13 or UPC-A package code. Calorie counters scan it and look up nutrition data.
Freemium
App with a permanent free tier and paid upgrades. Different from a free trial (which expires).
MAPE
Mean Absolute Percentage Error. Average of the absolute percentage gaps between predicted and actual values. Lower is better.
Paywall
App feature locked behind a subscription. The shape of the paywall (where it sits, what it gates) is more important than its existence.
Photo AI
Computer vision model that identifies foods from a photo and estimates portion size. Quality varies wildly between apps.
Validation Study
Independent test of an app's accuracy against ground-truth measurement. The DAI 2026 six-app study is the current gold-standard for calorie counters.