Camping means guarding a hooked survivor instead of leaving to pressure the rest of the map. Because a hooked survivor progresses toward death on a timer, simply standing nearby can trade one killer's time for one survivor's life plus the attention of whoever tries the save.
Like tunnelling, it is a legal strategy that is unpopular in casual play, and its strength depends heavily on how much map pressure the killer would otherwise have.
It has no meaning at all in 1v1 duels, where there are no hooks and no teammates - the term only applies to the 4v1 side of competitive play.