Diols are organic compounds that contain two hydroxyl (-OH) groups. They are also known as glycols and can be classified as either aliphatic or aromatic, depending on the structure of the carbon chain. Common examples include ethylene glycol and propylene glycol, which are widely used in antifreeze and as solvents. Diols play a significant role in various chemical processes and industries. They can be used in the production of polymers, such as polyesters, and are important in the synthesis of pharmaceuticals and other chemicals. Their unique properties make them valuable in both industrial and consumer applications.