There are multiple bands with that name:
1) A UK rock band from the 1970's.
2) A Swedish melodic rock band.
3) ユニコーン, a Japanese rock band.
4) The Dutch trance-producer Ron Van Den Beuken
5) The Belgian trance-duo Mauro Crisci & Tiziano Crisci
6) The Belgian trance-duo Philip Dirix & Prince Peration
7) Unicorn from Austria, medieval and early Renaissance music ensemble
8) The German (hard)trance and techno producer Sebastian Ostermann


Read more about Unicorn on Last.fm.