Casturbation relates to the art of masturbating whilst wearing a cast (caused from broken bones somewhere between the individuals wrists and shoulders).
It can often require a lot of patience and training depending on the size and location of the cast.

Watching porn via Google Chromecast.

the act of lotioning ones own cast (most often ones forearm cast) on the inside then inserting ones penis into the cast in a humping motion until climax is achived

verb. the act of pleasuring oneself with a broken arm.

Casting porn from your tiny phone/tablet to your giant TV screen via a streaming device (Chromecast, AppleTV, Roku, Fire Stick, etc.)

masturbating with a cast on, or using your hand with out the cast on to masturbate

When you break your arm/wrist/or hand that you normally use to masturbate with, and have to use the opposite hand to masturbate, because the cast you have to wear, hurts your dick.