The words boar, boer, bore sound the same but have different meanings and spellings. Why do boar, boer, bore sound the same even though they are completely different words?
The answer is simple: boar, boer, bore are homophones of the English language.
An uncastrated male pig.
The adult male of any of several mammals, such as the beaver, raccoon, or guinea pig.
The wild boar.
A Dutch colonist or descendant of a Dutch colonist in South Africa.
The caliber of a firearm.
A drilling tool.
To make a hole in or through, with or as if with a drill.
To form (a tunnel, for example) by drilling, digging, or burrowing.
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").