The words flock, floc sound the same but have different meanings and spellings. Why do flock, floc sound the same even though they are completely different words?
The answer is simple: flock, floc are homophones of the English language.
A flocculent mass formed in a fluid through precipitation or aggregation of suspended particles.
A group of animals that live, travel, or feed together.
A group of people under the leadership of one person, especially the members of a church.
A large crowd or number: had a flock of questions.
To congregate or travel in a flock or crowd.
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").