What it is
The segunda is bachata's second, rhythm guitar. It plays the chords and holds the harmony together with the bass.
The strokes
A bass note on 1, 3 and 4, following the bass guitar, and short strums on the chord on the other eighths.
What a dancer hears
The segunda sounds on every eighth and, like the güira, keeps an even grid. Its bass notes land with the steps on 1 and 3 and the tap on 4.