A mortise jig is a tool used in woodworking to create precise mortises, which are rectangular holes cut into a piece of wood. These mortises are often used to join two pieces of wood together, such as in furniture making or cabinetry. The jig helps ensure that the mortises are uniform in size and shape, making the assembly process easier and more accurate. Mortise jigs can be adjustable or fixed, depending on the design and the specific needs of the project. They are typically used with a router or a chisel to remove material from the wood. By using a mortise jig, woodworkers can achieve professional-quality results with less effort.