An expression invented by black people. Its literal meaning is "Sure, that would be swell!", but can also be used to express any happiness and excitement, which makes sense because black people are very easily excited.
"Yo, wana go eat some fried- C?" "Dayum foshizzles!"
"Omagah, i jus popped a nigga in da mouth and got dis lil trick right ova hurr!" "Dayum foshizzles!"