Musical form
It can mean: the kind of composition.  For example, a musical work can be a symphony, a concerto, a sonata etc.  This is more often called “musical genre”.  The word showing the musical genre will show things such as: whether the music is for an orchestra to play and whether or not there is a soloist as well, or whether it is a piece for one instrument on its own.  It may give an idea of whether it is likely to be a long piece or a short piece, or whether it has several movements.