Grabbing the edge of the board while in mid-air. The six basic grabs are the Mute Air, Indy Air, Stale Fish Air, Melon Nose and Tail Grab. Each grab has virtually endless permutations depending on exactly where one places one's hand on the edge and what one does with ones legs (known as "boning" or "poking") while in the air.
For instance, an indy grabbed between the back foot and the tail is known as a "tindy" (tail+indy) (and is seriously lame), while an indy grabbed close to the front foot with the board shifted backside is known as a crail. Likewise, a mute grab with the front knee tucked and back leg poked is a Japan Air, and a melon pulled back and shifted is a method. In addition to the six basic grabs and their variations are a whole host of different grabs.
A few tricks include:
See Snowboard Glossary for full list.