OrderedQ[h[, , ... ]] gives True if the are in canonical order, and False otherwise.
See notes for Order.
OrderedQ[e, e] gives True.
By default, OrderedQ uses canonical order as described in the notes for Sort.
OrderedQ[list, p] uses the function p to determine whether each pair of elements in list is in order.
See The Mathematica Book: Section 1.8.15 and Section 2.3.5.
See also: Signature, Sort.