upskirt

Short definition from Wiktionary

Adjective

1. 1
   Designating a voyeuristic image of the view up a woman's skirt.

Noun

1. 1
   An image of this kind.
2. 2
   The area inside a skirt, most commonly from below and while being worn.

Verb

1. 1
   To take a voyeuristic photograph up the skirt of (a woman), especially surreptitiously.