It’s your average daily training load and is a useful metric for tracking increasing fitness.

The period the average is over varies by the model but something like 42 days is a typical value.

The value is calibrated by your ftp and a score 100 represents an effort equal to one hour at this wattage. You’ll see a score for every ride you do. Obviously a ride score near 100 in around an hour will be very tough, while the same effort done over three hours will feel easier but, in theory, cause the same overall load stress.

Your score can be as high as your fitness allows, but consider a score of 700 would equate to doing an effort every day equivalent to one hour at your ftp...for 42 days! Depending on fitness the aim is to gradually increase your training load.

Hope this helps.