What does APR will vary with the market based on the prime rate mean?

It says my APR is 12.99%. But, then it says this APR will vary with the market based on the prime rate. The rate is actually very low right now. But, can someone clarify this statement? This is on a new credit card I’m receiving. Dan B- I have to get a credit card in [...] http://bit.ly/jYouVq