In organic chemistry, an epoxide is a molecule that has a ring with three atoms in total, of which two carbons and one oxygen atom. The ring looks like a triangle, with all edges of the same length. Because of this small ring, an epoxide is very reactive. It likes to be opened up by nucleophiles.
Epoxides can be made by oxidation of alkenes. There are many ways to do it. Usually, a peroxide is used. Some ways can even make only one enantiomer of the epoxide. Epoxides are useful because with them very complicated molecules can be made quickly. After opening the epoxide, an alcohol is left. This is also very useful, since it is easy to change the alcohol to many other functional groups.
Epoxides are extremely useful for the synthesis of loads of other compounds. That is because oxygen, which is in an epoxide, is such a great functional group. Once you have made an epoxide, you can make alcohols, ethers, and halohydrins, among other things.