Pickup shots are shots or scenes recorded after principal photography has concluded.
In some cases pickup shots are specifically planned. For example, on a film set, a scene may be filmed one day with the major actors and then the next day is devoted to pickup shots which do not require the actors. These shots could include close-ups of props, different angles in which the actors are not recognisable, etc.
In other cases pickup shots are unplanned shots which are needed to fix editing problems, re-shoot scenes for better quality, etc. As a contingency, time is usually allocated for pickup shots as part of the production plan.