Musical form
It can also mean: the shape of the music and how it is planned.  The form of a piece of music may, for example, be an “ABA” form, which means that there is the first part of the piece (which we can call part “A”), then something different happens (which we can call part “B”), and finally part “A” comes back again.  There are many other ways of planning a piece of music, e.g. in jazz there is the twelve bar blues (in which the music is based on a repeated pattern of chords that last 12 bars, or in classical music there is sonata form which can often be the plan of a movement lasting anything from five minutes (as in the early Classical symphonies) to half an hour (as in some of Mahler’s symphonies).