The equivalent of a single
record / CD single for audio cassette
s, that is a cassette with just one song on it.
is hard to find nowadays, even harder than prerecorded audio cassettes in general, which are on the decline anyway, due to CD
s and what not.
cassingle is not yet quite an official part of the English language (it's not in Merriam Webster's Dictionary, for example), but the term is used, especially in informal speech.