Definition of pre-orders:
(v) :
Alternative form of preorder. [(transitive) To order (goods or services) in advance, before they are available.]
(n) :
Alternative form of preorder. [An order for goods or services placed in advance.]
(adj) :
Alternative form of preorder. [(computing theory, of a traversal of a tree) Such that, recursively, the root is visited before the left and right subtrees.]