Groove

Groove is the propulsive rhythmic feel that makes you want to move, born from the precise interaction between rhythm-section instruments (drums, bass, guitar) rather than simply keeping tempo. A track that's perfectly in time metronomically can still "not groove".

A feel, not a measurement

Unlike a BPM tempo or a time signature, groove can't be read off a score: two guitarists can play the exact same notes at the exact same instants and produce a very different groove depending on how firm the palm mute is, how slightly ahead or behind each attack lands, or the chosen accents — it's a performance parameter, not a notated one.

The sheet rhythm groove riff — E minor is named that way precisely because the emphasis is on the feel of the pattern, not just the sequence of notes to play.