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.