Definitions

1. adverb

used to indicate a choice between two things, or one of two possibilities

“I’ll go to either the park or the movies, whichever you prefer.”

2. conjunction

used to indicate that something is one of two alternatives

“You can take either bus 12 or 15 to get to the city center.”

3. noun

one of two or more things, especially two

“The either of the two books on the table is mine.”