A pain score is a scoring system used by doctors to 'measure' and record the pain a patient is experiencing at any one time.
Pain scores for the knee
The most widely used pain score is the VAS score. VAS stands for 'visual analogue scale', where a person is asked to image 10 being the worst pain they can imagine and 0 being no pain at all. Then they estimate where their own pain would fit on such a line.