The words bald, balled, bawled sound the same but have different meanings and spellings. Why do bald, balled, bawled sound the same even though they are completely different words?
The answer is simple: bald, balled, bawled are homophones of the English language.
Lacking hair on the head.
Lacking a natural or usual covering: a bald spot on the lawn.
Lacking treads: a bald tire.
Zoology Having white feathers or markings on the head, as in some birds or mammals.
Simple past tense and past participle of ball.
Simple past tense and past participle of bawl.
Definitions from The American Heritage® Dictionary of the English Language, 4th Edition, from Wiktionary, Creative Commons Attribution/Share-Alike License and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.
If they are spelled the same then they are also homographs (and homonyms); if they are spelled differently then they are also heterographs (literally "different writing").