What is the difference between an accoustic guitar and a bass?

The lower four strings on an accoustic guitar are a few octaves higher, but the same notes as a bass guitar. Bass guitars are usually 4-string, the strings are MUCH thicker and all are wound, they have a longer neck and they're usually electric. I believe that most bass players pluck the strings with their fingers (no picks). Acoustic guitars are usually 6-string, the lower four strings are usually wound around a core wire and the upper 2 usually single strands (though nylon strings are also available), they have a "box" that provides the sound though now-a-days, many have pickups and are capable of being attached to an amp, and there are different tones created by finger-picking and using a pick.

A bass guitar has a lower octave range, and usually only 4 strings. A standard acoustic has 6 strings and a higher octave range.