Hedonism is a type of philosophy. Hedonism can be generally summed up as a belief that "pleasure is the highest good" or that "whatever causes pleasure is right."
In Hedonism, people think that what makes them happy is good. Things that avoid pain are also good. Hedonism is focused around pleasure. There are different beliefs in hedonism. Some people believe it is important to get as many pleasurable experiences as possible, others believe that the quality of the pleasure matters. They think there are higher and lower pleasures. Some well known Hedonists were John Stuart Mill and Jeremy Bentham.
Many people also believe Hedonism is related to sex. This is not true. Sex can be a very pleasurable experience, but when philosophers talk about Hedonism, they think more about the pleasure of reading a good book, listening to classical music, or discussing with other philosophers.
Two types of Hedonism are Cyrenaicism and Epicureanism. Cyrenaicism is where people make themselves happy in the fastest amount of time. Epicureanism is where people like to be happy but they do so slowly so that they cause less pain to themselves. They also look more into the future and go for the higher pleasures in life.