Objective mode was a holodeck setting which allowed users to observe characters and events in the program without interacting with the holographic environment. When objective mode was activated, holodeck characters would not take notice of the user, and the user could pass through solid objects, such as doors and bulkheads. This was the opposite of subjective mode.
In 2370, while running an historic holoprogram on the USS Enterprise-D depicting the final voyage of Enterprise NX-01, Commander Riker used the objective mode feature to observe interactions among the characters when not taking on the role of an Enterprise crewman. (ENT: "These Are the Voyages...")