Collage adhesive is a material used to attach items together in a collage. It can be either PASTE or GLUE, both of which are commonly used for this purpose. PASTE is a thick liquid that is applied to the back of an item and then pressed onto the surface of the collage. GLUE is a sticky substance that is applied to the back of an item and then adhered to the surface of the collage. Both PASTE and GLUE are effective adhesives for creating collages.