Rubber cement is an adhesive made from elastic natural polymers, typically latex mixed in a solvents.
These cements are considered drying adhesives, meaning that as the solvents evaporate, the "rubber" portion remains behind, ready to form a strong and flexible bonds. There are even paper specific rubber cements, used by paper crafters and scrapbookers. Rubber cement is unusual in that it can be either a reposition-able or permanent bond.