A coffin was a container in which a dead corpse was buried.
Life pods resembling coffins were sent through the Cardiff Space-Time Rift by the xXltttxtolxtol. They planned to use them help invade Earth. They were stopped by Torchwood Three. (PROSE: Risk Assessment)
When the Shansheeth's memory weave overloaded, Sarah Jane Smith and Jo Jones were able to save themselves by taking shelter in a lead-lined coffin that supposedly contained the Eleventh Doctor's remains. (TV: Death of the Doctor)