What is it?
Just as the name suggests, an acoustic guitar is similar to a normal acoustic guitar. According to Wikipedia, the name is sometimes shortened to Acoustic Bass. It has a hollow wooden body which is used to amplify the sound. A typical acoustic bass guitar has four strings which are tuned as E A D G, but some other times you may find it with 5 or 6 strings. It is a little bit larger than the normal acoustic guitar.
The Acoustic Bass may not be audible enough for big crowds, therefore most of them have sound pickups fitted on them. This means that you can choose to use amplifiers on them for sound amplification.