Bass Guitar
The main function of a bass guitar is laying down the beat and anchoring the harmonic framework in different types of music (pop, (punk) rock, metal, blues, jazz and country) but it is a great solo instrument as well.
Basically, a bass guitar looks the same as a normal guitar but has a larger body and longer neck and scale length. Most bass guitars have 4 strings which are thicker than regular guitar strings and are tuned the same as the four lower strings on a 6 string guitar (E A D G), only an octave lower.
There are also 5 and even 6 string bass guitar available, which provide extended lower range and makes the instrument highly versatile.
Most bass guitars have frets (just like a guitar) but there are also fretless bass guitars available.
Learn more about cleaning a bass guitar here.