The term preorder may refer to:
In mathematics: Preorder, a reflexive, transitive relation Preorder field, a field of sets structure on a set with preorder Preordered field, a field with a preorder Preordering, a vertex ordering from a tree or other graph traversal; see Depth-first search#Vertex orderings
In marketing: Pre-order – an order placed for an item which has not yet been released.