WordNet (r) 3.0 (2006):

ponytail
    n 1: a hair style that draws the hair back so that it hangs down
         in back of the head like a pony's tail

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

ponytail
 n.

    1. A hairstyle in which long hair is held back so as to hang down like a
    pony's tail.

    2. A descriptive term for a man having a ponytail hairstyle, or such
    character traits as might be associated with having a ponytail, eg:
    effeminacy, narcissism, undue concern with fashion etc.

    3. A general term used by hackers for 'creatives': advertising copywriters,
    graphic designers, video compositors, users characterised by a preference
    for the Macintosh, recreational drug use, and better sex lives than
    programmers.

    4. A derogatory term for web designers and other persons peripherally
    associated with IT projects, devoid of programming skills and dismissed as
    being concerned with visual presentation to the exclusion of actual
    technical reality.