An adhesive, also known as glue, is a material, typically liquid or semi-liquid, that adheres or bonds items together. Adhesives come from either natural or synthetic sources. The types of materials that can be bonded are vast but adhesives are especially useful for bonding thin materials. Adhesives cure (harden) by either evaporating a solvent or by chemical reactions that occur between two or more constituents.
Adhesives are useful for joining thin or dissimilar materials, minimizing weight, and providing a vibration-damping joint. A disadvantage of most adhesives is that most do not form an instantaneous joint, unlike many other joining processes, because the adhesive needs time to cure.
The earliest known date for a simple glue is 200,000 BC and for a compound glue 70,000 BC.
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