The words sights, sites, cites sound the same but have different meanings and spellings. Why do sights, sites, cites sound the same even though they are completely different words?
The answer is simple: sights, sites, cites are homophones of the English language.
Plural form of cite. citations
Third-person singular simple present indicative form of cite.
Plural form of sight.
the things worth seeing in a particular place
the devices through which one looks in order to aim a rifle or similar weapon
Third-person singular simple present indicative form of sight.
Plural form of site.
Definitions 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").