SharpShooter wrote:
1955, welcome to the Hog!
It means it's a zoom lens. That means it can change(zoom) its focal length between 75mm(a fairly short telephoto length) to a 300mm(a medium tele length) and everything in between.
I'll assume that the 600d is a crop camera, so it's worth mentioning that the lens actually has the same angle of view, on your camera, as a lens 1.6x that long as the same lens on a FF camera. ;-)
SS