Alternatively spelled mitre, this joinery type occurs when the edges of two pieces are cut at angles as to fit together. Because you see them on art and photo frames everyday, the most ubiquitous type of miter joint is the combination of two 45-degree cuts made to form a 90-degree corner. What holds the pieces together varies. Depending on the level of stress/force that will be applied to the joint, it could be nothing but glue or a combination of adhesive with splines, biscuits, tacks, fasteners, etc.