The words Inc., ink sound the same but have different meanings and spellings. Why do Inc., ink sound the same even though they are completely different words?
The answer is simple: Inc., ink are homophones of the English language.
incorporated
A pigmented liquid or paste used especially for writing or printing.
A dark liquid ejected for protection by most cephalopods, including the octopus and squid.
Informal Coverage in the print media; publicity: Her campaign rallies generated a lot of ink.
To mark, coat, or stain with ink.
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").