The standard bass guitar has 4 strings. These are pitched an octave lower than the corresponding strings on a guitar which gives them a deeper sound. Basses also commonly exist in five-string and even six-string versions.
Bassists tend to anchor the harmony of the song by highlighting the roots of a chord progression. This helps to establish the key of the song.
The bass guitar, along with the drums and rhythm guitar, make up the rhythm section of a band. The bass contributes significantly to the beat and groove of the song, making timing particularly important to proper playing.
In jazz, the bass guitar is used for accompanying like in rock, but also tends to play a more prominent role in soloing.
The first widely produced electric bass was Leo Fender's Precision Bass, which was issued in the early 1950s. The invention of the electric bass was a great relief to traveling musicians, who had been burdened with carting around the monstrous double bass.