A time contour was a method of time traveling in which a "tunnel" stretched through time from the destination to the departure, linking the two time periods.

The Master, after escaping from Castrovalva and becoming trapped on prehistoric Earth, used parts from his TARDIS to create a time contour. He was able to bring a Concorde from 1982 to prehistoric times so that he could use the passengers to break into the sanctum and use the Xeraphin gestalt to power his TARDIS.

The Doctor was able to rescue the passengers and stop the Master from taking the Xeraphin. (It can be assumed he closed the time contour too.) (DW: Time-Flight)