That's correct Badger. Ever since I had kidney cancer it's been a figure close to my heart, if that doesn't sound contradictory).
They say that it indicates how well your kidneys function as a percentage, but don't get over excited if you're not 100% – no one is.
Unless it's very low no one will get too excited – say 20% or so, but you can live quite happily at 30%. What will concern them more is any sudden unexplained drop. Another thing to take in to account is that it can vary quite widely between readings.
There seem to be many readings they take that when they are out of line they ignore, but that's probably because there'll be obvious physical symptoms if you have a problem. It's just something they monitor.
Mine's varied between 50% and 70% more recently over the years and I doubt that my kidneys are improving with age. Anyone's reading should deteriorate over time.
