A small hole in a pipe, bong, or other smoking device with a smoke holding chamber. Located at the end of the chamber farthest from the smoker's mouth. A thumb or finger is placed over the hole during the initial inhalation so that smoke can be sucked into the holding chamber. After the chamber is filled with smoke, the choke is released and the smoke sucked out of the chamber with fresh air rushing in through the carb to displace it.
Shit man, you lied. You've never smoked before. You didn't even know enough to hold the choke!