What it is
The piano in salsa plays the montuno: a repeating figure of chords and octaves, written to fit the clave. With the bass it sets the song's harmony.
The strokes
Chord: several notes at once, short. Octave: one note of the chord in both hands, an octave apart.
Push: the next chord played on the & of 4, before the bar begins, and left ringing over the 1.
The 3-2 and 2-3 montunos are one pattern started from different bars. In a bolero the piano plays the chord on 1 and again on the & of 2.
What a dancer hears
The montuno goes round and round through the whole song — the most recognizable part of the rhythm section. The push on the & of 4 (with the bass) makes the 1 feel like it has already arrived, so the step on 1 in salsa sounds like landing after a pickup.