Homophones are words that have exactly the same sound (pronunciation) but different meanings and (usually) spelling.
For example, the following two words have the same sound, but different meanings and spelling:
hour
our
Usually, homophones are in groups of two (our, hour), but occasionally they can be in groups of three (to, too, two) or even more. If we take our bear example, we can add another word to the group:
bear (noun: large, heavy animal with thick fur)
bear (verb: tolerate, endure)
bare (adjective: naked, without clothes)