What exactly is "digital heat transfers"?

Digital Heat Transfers - Using digital printers (inkjet printers, thermal wax printers, etc.) to print a design on a special paper. The printed design is then applied on the substrate using a heat press.

Screened Heat Transfers - Using a traditional screen printing press to print a design on a special paper. The printed design is then applied on the substrate using a heat press. For mass production, flat-bed presses with vacuum table is optimal

Of course there are more differences, but that's basically the gist of it.

Great explanation Marc! Very helpful.

what about doing heat transfers on poly/spandex fabric? if not heat transfer what is the best print method?

Are the digital transfers more crisp and clean looking than the screened transfers? It always seemed to me that the screened ones don't look as clean or maybe I'm just encountering a poor product.