APRC stands for "annual percentage rate of charge". You'll see an APRC percent with the information you get when you're recommended a mortgage.
APRC aims to show you what the average interest over the whole mortgage term would be, by combining your initial fixed interest rate with your lender's standard variable rate (SVR), which you're put on after your initial term ends if you don't remortgage.
But that's the thing: APRC assumes you'll never remortgage, even though remortgaging will almost always get you a better rate than an SVR. So it’s usually safe to ignore APRC if you're planning to review your mortgage options after your initial rate expires.