reciprocal (adj.): given or done in return; [grammar] expressing mutual action
We use reciprocal pronouns when each of two or more subjects is acting in the same way towards the other. For example, A is talking to B, and B is talking to A. So we say:
The action is "reciprocated". John talks to Mary and Mary talks to John. I give you a present and you give me a present. The dog bites the cat and the cat bites the dog.
There are only two reciprocal pronouns, and they are both two words:
When we use these reciprocal pronouns:
Look at these examples:
You probably notice that each other is used in more examples above than one another. That's because in general we use each other more often than one another, which sounds a little formal. Also, some people say that we should use one another only for three or more people or things, but there is no real justification for this.