If your league area has a Topgun or MVP program and publishes it on member services, rank would be your standing in that program.
These programs differ from area to area. Some use winning percentage, some use "Topgun" points (sum of the skill levels of the players you beat), some use a slightly different formula. Some are tiered (and the tiers may differ) by skill level groups and some are not. Whatever the program is for your area, if there is one and it is published, rank shows where you stand.