This is a term mostly used by those involved with Wheel of Fortune. It means fantastic, but the "fan" is changed to "spin", referencing the wheel in the popular game show. Pat Sajak, the host, has said this phrase a few times, which is how it stuck with the audience.
1.) Someone or something so sexy that it makes you want to spank the monkey.
2.) An ass so fine that when you see it you want to give it a smack.
3.) A severe bitch-slap beat down.