g/l stands for gain and loss. If you do 5,000' of ascent and return you are covering 10k of gain and loss. It is a way to meter how taxing a route is. Downhill taxes you too. Not the same way, but it does. If you do i2b2i you actually do 12,100 of gain, and 12,100 loss (as you repeat every downhill/uphill returning, in reverse).
20k was a ballpark figure of g/l
