Everybody means all the people in a particular group or situation. When your teacher says everybody needs to turn in their homework, she means every single student in the class. When you announce that everybody is invited to your birthday party, you're including all your friends and classmates.

The word works like “everyone,” and both mean the same thing. You might say “everybody loves pizza” when describing something popular, though of course some people genuinely don't. This kind of statement uses everybody for emphasis rather than literal accuracy.

Notice that everybody is singular in grammar, even though it refers to many people. You say “everybody is here” not “everybody are here.” This trips up many writers.

When someone claims “everybody thinks that” or “everybody does it,” it's worth thinking carefully. People sometimes use everybody to pressure others into going along with the crowd, even when it isn't true that everyone actually agrees.