Michael Jordan, of basketball fame, appeared in a series of ads for Hanes underwear using the term "tagless" to denote that there was not a sewn label in the neck of the garment. More correctly this is called a heat transfer but these two words are not as descriptive as "tagless". Heat transfers are a great option vs. a sewn-in label anytime the garment is in direct contact with the skin.
A transfer is a combination of an adhesive base and an ink top layer placed on a release sheet. When heat is applied with pressure the adhesive bonds to the fabric and the ink further fuses with the adhesive. The carrier sheet is then peeled away leaving the transfer affixed to the fabric. Depending on the fabric , various combinations of adhesive, ink and dwell time are used to insure optimum performance and serviceability. We can always test your fabrics to determine the best results.