The Collaborative International Dictionary of English v.0.48:

Intro- \In"tro-\ [L. intro, adv., inwardly, within. See
   Inter-.]
   A prefix signifying within, into, in, inward; as, introduce,
   introreception, introthoracic.
   [1913 Webster]

WordNet (r) 3.0 (2006):

intro
    n 1: formally making a person known to another or to the public
         [syn: presentation, introduction, intro]
    2: a brief introductory passage to a piece of popular music

The Jargon File (version 4.4.7, 29 Dec 2003):

intro
 n.

    [demoscene] Introductory screen of some production.

    2. A short demo, usually showing just one or two screens.

    3. Small, usually 64k, 40k or 4k demo. Sizes are generally dictated by 
    compo rules. See also dentro, demo.