When a player intercepts the ball, he has a chance to run with it to gain additional yards. An interception touchdown happens when a player intercepts a ball and returns it all the way to the other team's end zone and scores a touchdown.
There are several slang terms for interception touchdowns, including "pick six" and "house call". Rod Woodson holds the record for most interception touchdowns in a career. Charles Woodson has the most consecutive seasons with interception touchdowns with 6 seasons from 2006-11, all with the Green Bay Packers.