Art & Prepress
Transparent Background
A transparent background is an image file saved with no background color at all, so only the design prints and the shirt shows through everywhere else.
PNG and a handful of other formats can store an alpha channel — a transparent background — marking certain pixels as fully or partially see-through instead of filling them with white, black, or any other color. Open a transparent PNG in an editor and a checkerboard pattern behind the artwork signals nothing is there; open a JPEG, which can't support transparency at all, and there's always a solid background color filling every pixel.
For a buyer, this is the difference between a logo that sits cleanly on a shirt and one that shows up as a white rectangle stamped over the fabric. We've received plenty of "clean" logo files pulled from a web search that looked transparent on-screen against a white webpage, only to reveal a solid white box the second they got placed on a navy or black shirt in a mockup.
Pros ask for a PNG with a genuine alpha channel, or better, a vector file with no background object at all, rather than trusting a file that merely looks background-free against a white screen or webpage. For DTG and DTF printing especially, a true transparent background is what lets the printer knock out everything except the design itself and lay it directly onto the garment color.
The common mistake is assuming a white background and a transparent one look the same, since both can appear blank against a white screen or in a white email preview. They're not: one is invisible everywhere, the other is a solid white shape that prints as part of the design on anything but a white garment.