HD stands for "high definition". HD lace is a royal lace material that used to be called Swiss lace, and which is invisible when applied to the scalp. This ensures that the wig-wearer can have an exposed hairline, which looks very natural and renders the lace along the hairline highly undetectable. The lace closures are designed to give you a natural looking part w/o having to leave your natural hair or or adding any excessive heat, glue or any other damaging products to your real hair. Dimensions 5x5 Lace Closure