The words jab, jabb sound the same but have different meanings and spellings. Why do jab, jabb sound the same even though they are completely different words?
The answer is simple: jab, jabb are homophones of the English language.
Sports A short straight punch in boxing.
To poke or thrust abruptly: jabbed a knife into the log.
To stab or pierce: jabbed the steak with a fork.
To punch (someone) with short blows.
Definitions 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.
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").