While it may seem a little less than erudite, a term used quite commonly on record jackets and in books within the appropriate genre is just "talkin' blues." (talkin' as an adjective, not a verb)

Of course for anything other than the blues one would likely want to seem a little more "literate" (???), but I can't think of anything more descriptive that I've heard used very often.

In sheet music, the notation is usually just "[Spoken]" which seems more an instruction than a description.

John