Definition of a 'Tee'
Here is the definition of a Tee.
A 'tee' is a device designed to raise the ball off the ground.
It must not be longer than four inches (101.6 mm) and it must not be designed or manufactured in such a way that it could indicate the line of play or influence the movement of the ball.
Taken from the Rules of Golf - 2008 - 2011 Edition (page 42)