They are synonyms, both very similar. How ever there is a small difference, people normally use them it different situations. A "hoax" is deception; it is called a hoax when a newspaper knowingly prints a fraudulent story, business scams, bogus political claims, false bomb threats, misleading stunts in public, UFO conspirators and scientific frauds. Basically used for deceitful means, like fraudulently obtaining personal details or money. While a "prank" tends to less serious and more for mischievous means, like a small joke just for laughs. For example, placing a whoopee cushion on someone's seat. Hope this helps

Sometimes they mean the same thing. But a "hoax" is always to make people believe something false. It's thought of as more serious, and usually affects many people. A "prank" can do that. But a prank can be a childish trick played on one person, like tricks children play on each other at school. A prank is thought of as less serious, and affects one (or few) people.

A hoax is very elaborate and complicated. A prank is more brutish, and can be performed by an unskilled person; a prank also implies a stupid, crass action by someone. A hoax is more like fraud, when someone does a good job of deceiving you. :)