1. [n]  a creation of the highest excellence
2. [n]  an artist who has created classic works
3. [adj]  characteristic of the classical artistic and literary traditions
4. [adj]  adhering to established standards and principles; "a classic proof"

1. \Clas"sic\, Classical \Clas"sic*al\, a. [L. classicus
   relating to the classes of the Roman people, and especially
   to the frist class; hence, of the first rank, superior, from
   classis class: cf. F. classique. See {Class}, n.]
   1. Of or relating to the first class or rank, especially in
      literature or art.
            Give, as thy last memorial to the age, One classic
            drama, and reform the stage.          --Byron.
            Mr. Greaves may justly be reckoned a classical
            author on this subject [Roman weights and coins].
                                                  --Arbuthnot.
   2. Of or pertaining to the ancient Greeks and Romans, esp. to
      Greek or Roman authors of the highest rank, or of the
      period when their best literature was produced; of or
      pertaining to places inhabited by the ancient Greeks and
      Romans, or rendered famous by their deeds.
            Though throned midst Latium's classic plains. --Mrs.
                                                  Hemans.
            The epithet classical, as applied to ancient
            authors, is determined less by the purity of their
            style than by the period at which they wrote.
                                                  --Brande & C.
            He [Atterbury] directed the classical studies of the
            undergraduates of his college.        --Macaulay.
   3. Conforming to the best authority in literature and art;
      chaste; pure; refined; as, a classical style.
            Classical, provincial, and national synods.
                                                  --Macaulay.
   {Classicals orders}. (Arch.) See under {Order}.
   

2. \Clas"sic\, n.
   1. A work of acknowledged excellence and authority, or its
      author; -- originally used of Greek and Latin works or
      authors, but now applied to authors and works of a like
      character in any language.
            In is once raised him to the rank of a legitimate
            English classic.                      --Macaulay.
   2. One learned in the literature of Greece and Rome, or a
      student of classical literature.
   

An adjective used before or after a noun to describe the original version of something. This construction is especially used of product series in which the newer versions are considered worse than the older ones.

Examples include "Star Trek Classic" - the original TV series as opposed to the films, ST The Next Generation or any of the other spin-offs and follow-ups; or "PC Classic" - IBM's ISA-bus computers as opposed to the PS/2 series.