Phase cancellation, the effect of two waves that are out of phase with each other being summed

"Cancelled" (South Park) an episode of South Park.

Cancellation (mail), in mail, a postal marking applied to a stamp or stationery indicating that the item has been used

Loss of significance when doing calculations with floating point numbers.

Cancellation (television), the termination of a television series

Cancellation property, the property that if a * b = a * c then b = c

Cancellation of removal, a form of immigration relief available to aliens in the United States who be otherwise inadmissible or deportable.

Cancel character, in telecommunication, an indication that the data with which it is associated are in error or are to be disregarded

Cancel message, in Usenet, a special message used to remove articles posted to news server