A common term for 'canned' air; a spray can containing a complex liquid chlorofluorocarbon (these days, sometimes one engineered not to harm the ozone layer) which, when released from the pressurized can, shoots out at high speed as a gas. The term comes from the first use of this stuff, which was to clean sensitive photo equipment and supplies. Nowadays, the computer industry lives on it, for cleaning keyboards, components, etc. etc.