Is a wonderful new process that allows you to print on a special transfer paper / vinyl allows a full colour image to be transferred onto the shirt. The image is transferred onto a paper via silkscreen of printed onto a special stretch vinyl that is suitable for t-shirts and fabric. The Vinyl is a very affordable way of doing a few t-shirts whilst the silkscreen requires positives and screens to be made. The benefit of the silkscreen paper is that you can print the paper an heat press it only when the order is made. Vinyl can be used exactly in the same way.
For large quantities silk screening is better.
Also see sublimation printing, silkscreen printing, vinyl printing