The words ha ha, ha-ha sound the same but have different meanings and spellings. Why do ha ha, ha-ha sound the same even though they are completely different words?
The answer is simple: ha ha, ha-ha are homophones of the English language.
Expression of laughter.
A sound made in imitation of laughter.
Slang An instance of amusement. Often used in the plural: drove past the old school just for ha-has.
Used to express amusement or scorn.
See sunk fence.
Definitions from Wiktionary, Creative Commons Attribution/Share-Alike License, from The American Heritage® Dictionary of the English Language, 4th Edition and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.