A print release is basically a document that allows your client to make other prints, including on various material(s) of the images they have received from you, the photographer. However, one key thing to keep in mind is that a print release is specifically geared to personal usage. This means that the images can be used on social media, on canvases and t-shirts and to a certain extent be shared with family.
The client does not have the permission to edit the image, make a derivative of the image, claim the work as their own, and most importantly cannot use the image for commercial gain! In order to do any of these things, a print release is not enough. The client would then have to get copyright permission.
As a photographer, it is absolutely important that you make sure your client understands that a print release is not the same as a copyright transfer or release and what each type of release grants them.
To take a look at the print release head over to PPA.com/contracts.