Don't know if this is the right section of the forum to post this.

I tried finding its definition in the help as well as rules pages, but did not find anything.

Wikipedia says, "In music, a single or record single is a type of release, typically a song recording of fewer tracks than an LP record, an album or an EP record."

Does a song not contained in any album but released on YouTube count as a single? Basically, what is a single?

Thanks!

Youtube singles are not valid releases since they are not downloadable. Some more details on (digital) singles here.