Bis is a Latin prefix or suffix designating the second instance of a thing, thus preceding ter. An example in recent modern usage is the ITU-T modem standard from the late 20th century, V.32bis. Bis can also refer to:
Pachelbel's Canon in D major, a piece of chamber music scored for three violins and basso continuo and originally paired with a gigue in the same key, experienced a tremendous surge in popularity during the 1970s.
In the Western tradition of music, there are basically twelve keys, corresponding to the twelve notes of the chromatic scale on a keyboard instrument (ie C, C#, D, D#...etc all the way up to C again). But as these can be either major or minor, we end up with a total of 12 major + 12 minor = 24 possible keys.