Jank
Visible stutter in scrolling or animation, caused by frames that take longer than the display's frame budget.
Definition
At 60 Hz the app has about 16 ms to produce each frame, at 120 Hz about 8 ms. Work on the main thread, heavy recomposition or layout, and garbage collection pauses can push a frame past that budget, so it is shown late or skipped. Jank is measured on release builds on real devices, with tools such as Macrobenchmark, Perfetto and JankStats.
In practice
Formatting prices inside a composable on every scroll frame makes the product list stutter on mid-range phones.