These are how the related sets of pictures of nekkid wimmin are often referred to by afficionadoes of skin mags.

Actually, it can mean any set of related pictures, usually in a magazine photo-article, or what Mr. Webster dude says.

Pic*to"ri*al (?), a. [L. pictorius, fr. pictor a painter, fr. pingere to paint. See Paint.]

Of or pertaining to pictures; illustrated by pictures; forming pictures; representing with the clearness of a picture; as, a pictorial dictionary; a pictorial imagination.

© Webster 1913.