Themselves is a pronoun people use to refer back to a group of people (or sometimes one person) already mentioned in a sentence. When you say “The students prepared themselves for the test,” themselves points back to the students. It means they prepared their own selves.

The word has two main uses. First, it emphasizes that people did something on their own: “They built the treehouse themselves” means nobody helped them. Second, it shows that people are both doing an action and receiving it: “They blamed themselves for the mistake” means each person blamed their own self.

You'll also hear themselves used to refer to a single person when you don't know or don't want to specify that person's gender. If someone finds a lost wallet, you might say “They should return it themselves” even though you're talking about just one person. This usage has become more common in everyday English.

The word works the same way for people that itself works for things or myself works when you're talking about yourself. These are all reflexive pronouns, words that reflect back to someone or something already mentioned.