Temporal mines were a weapon created by the Daleks for use in the Last Great Time War. They were placed in another pocket of space and would wait for a large enough enemy force to pass by before detonating, wiping them out. The Time Lords collected many temporal mines and repurposed them to use themselves against the Daleks.
The Tenth Doctor encountered a temporal mine after it attacked his TARDIS. (PROSE: Keeping up with the Joneses)