About

The bass guitar is a stringed instrument played primarily with the fingers or thumb (by plucking, slapping, popping, tapping, or thumping), or by using a pick.

The bass guitar is similar in appearance and construction to a guitar, but with a longer neck and scale length, and four, five, or six strings. The four-string bass—by far the most common—is usually tuned the same as the double bass, which corresponds to pitches one octave lower than the four lower strings of a guitar (E, A, D, and G). The bass guitar is a transposing instrument, as it is notated in bass clef an octave higher than it sounds (as is the double bass) to avoid excessive ledger lines.

(From Wikipedia)