Cheeksneak

When a girl is wearing a skirt or shorts that reveal the under-curve of her asscheek she is offering a cheeksneak.

When a girl moves or walks a certain way and her clothing accidentally reveals her ass; a sneak-peek at her cheek.

Similar to a nipslip only for asses.

"Those shorts give a nice cheeksneak on that girl."

"Cheeksneak is the new sideboob."