The term t-shirt is a short form for tee-shirt. This name is given to tee-shirts because of the shape of the clothing when laid down flat (it looks like a T). In the US, tee-shirts(or t-shirts) are...
Yes, you need a license from the owner of the copyright, which is normally the music publisher that controls the rights to the song. Reprint on anything, whether it be paper, a t-shirt, or anything...