Metasturbation is the practice of masturbating while thinking of yourself masturbating. This can be achieved simply through thought, or with mirrors or previously recorded photographs or videos of yourself masturbating.
"Dude, I walked in on my roommate metasturbating. He was blowing his load on a picture of his own face."
"Gosh, I love metasturbation. It's almost like getting myself off two times at once."