Definitions
1.nounAn order for goods or services placed in advance.
2.nounA binary relation that is reflexive and transitive."The relation of logical implication over sentences is an example of a preorder."
3.verbTo order (goods or services) in advance, before they are available.
4.verbTo sort or arrange beforehand.
5.adjective(of a traversal of a tree) Such that, recursively, the root is visited before the left and right subtrees.