Offensive Range is a way to categorize players into groups (Perimeter, Midrange, Paint) that indicate what area on the floor they likely operated in most of the time. It's a key component in determining the effects of the Defensive Positioning setting.
For example, a player labeled as Perimeter would be affected negatively by an opposing defense playing a +3 positioning. A Midrange player would still be affected negatively on 3pt shots, but would experience a positive effect on 2pt shots. A Paint player would perform very well against a +3 defensive setting. The opposite would hold true for a -3 Defensive Positioning.
The Offensive Range designation is determined by a formula based on percentage of FGA that are 3pt shots, assists per minute, offensive rebounding, and position. So a player's range may vary from season to season depending on how the stats indicate they played that season.