Multi-Doctor story
From Tardis Wiki, the free Doctor Who reference
In common fan parlance, a multi-Doctor story is one that involves multiple incarnations of the Doctor. Typically, although not necessarily, such episodes are reserved for anniversary and/or charity events. The term is not usually applied to stories like The Almost People which involves a doppelgänger, or Father's Day, which has multiple instances of a single incarnation.
Multi-Doctor stories included:
