Any liquid, mucilage, or paste that can be applied to one or both surfaces of two objects and that will cause those surfaces to adhere when they are brought into close contact, making a permanent bond.
Mike Allaby
Internet
Any hardware or software which is used to connect two software or hardware entities; for example, software which enables a Web server to communicate with some non-standard software such as an arcane database management system. It is often used to describe hardware or software converters which mediate between two protocols.