The word "either" is used to indicate a choice between two options, possibilities, or alternatives. It signifies that one option is to be selected or that one of two statements is true. For instance, you might say, "You can have either tea or coffee," meaning you can choose one of those two drinks.
The term "either" traces back to the Old English word "ǣgðer," which means "each of the two." It has Germanic origins, sharing roots with similar words in other Germanic languages.