collection of musical pieces; album; suite; studies
Refers to a published collection of musical compositions, such as an album, a set of études, or a suite. The specific nuance depends on context.
This collection contains works by Bach.
I bought a book of piano studies.
曲集 is the usual term for a collection of musical pieces or songs, whereas 歌集 in this sense is less common and mainly used for classical or folk song collections.
Compound of 曲 (kyoku, 'musical piece') and 集 (shū, 'collection').