buy / by / bye are similar-sounding terms with different meanings (referred to as homophones). To better understand the differences, see below for definitions, pronunciation guides, and example sentences using each term. 👇
buy: (verb) obtain by purchase; acquire by means of a financial transaction. (verb) be worth or be capable of buying. (verb) acquire by trade or sacrifice or exchange. (verb) accept as true.
by: (adverb) so as to pass a given point.
bye: (noun) you advance to the next round in a tournament without playing an opponent.
buy: b·AY
by: b·AY
bye: b·AY
(Examples are Wikipedia snippets under the CC ShareAlike 3.0 license. Definitions drawn from WordNet.)