Seen here is a borderless dry-mount option. One could also use the mat board as both the artwork backing and the border by using a top-mount method.
Artwork is dry-pressed on board which is then secured to background mat board to create a float like effect.
Window cut is a classic technique used for high-end framing. It allows the artwork to sit beneath a mat board with a window cut. This can be used in conjunction with one or more other mats (double mat, triple mat, etc). Artwork is either dry-pressed to board or adhered with linen tape and the hinge method.