Cell phones have GPS on them how accurate are they on them?

I have a cell phone and I activated the GPS on it and have it so I can check the location on my computer. How accurate are they? In some cases it says accuracy 8 and some it says 6. So does that mean that the person with the phone is in that location or in the vicinity? I understand that it bounces off of satellites and stuff. I have it to check it every 15 min. So what does the 8 and 6 really mean?