beat
The steady pulse under music, the thing your foot taps.
The steady pulse under music, the thing you tap your foot to and count off before a song starts. Beats group into bars, and their speed is the tempo. Everything rhythmic is measured against this grid, even when the music plays against it (see syncopation).
Learn it: Organizing time · The piano roll
The one-sentence definition at the top is the same one the Theory Aide extension shows as a tooltip inside Ableton Live. Hover any dotted term for its own.