Activating Prior Knowledge refers to the practice of beginning a lesson by bringing up topics with which the students already have some familiarity. By putting the upcoming lesson material into a familiar context for the students, the teacher is giving them a context into which they can then assimilate the new information and understanding.
This discussion can also be used to gauge the level of prior knowledge of the students which can inform how to proceed with your instruction.
Activating Prior Knowledge can be included as part of the Anticipatory Set.
As the teacher began her lesson on Marine Life, she briefly discussed Shamu, the orca at Sea World, since she knew that all of the students had visited Sea World before. The students then had a basic image in their minds of underwater life before she introduced them to the new types of marine life in the Oceanography unit.