Each other is a phrase that describes a mutual or two-way action between people or things. When two friends help each other with homework, one helps the friend and the friend helps back. When basketball players pass to each other, the ball goes back and forth between them.

The phrase emphasizes the back-and-forth nature of the interaction. If you say “The siblings argued with each other,” you mean both were arguing, not just one yelling while the other stayed silent. When teammates trust each other, that trust flows both directions.

You'll often see each other in sentences about relationships and interactions: people who respect each other, teams that depend on each other, or neighbors who wave to each other in the morning. The phrase captures the idea that both sides are equally involved in whatever is happening.

Writers sometimes confuse each other with one another. Traditional grammar rules suggest using each other for two people or things and one another for three or more, but most people use them interchangeably today. Still, if you want to be precise: “The two captains shook hands with each other,” but “All five teammates congratulated one another.”