BSS (Basic Service Set) Mode, also known as InfrastructureMode, is where 802.11b wireless clients talk to each other via an AccessPoint. This is as opposed to AdHocMode where clients talk to each other directly.
The main advantage of BSS Mode is that two clients that can't directly see each other, but who can both see the central AccessPoint can still talk to each other. This doubles the maximum effective separation between clients with respect to an ad hoc network.
JouniMalinen has written a Linux Host Ap Mode driver that works with this card to provide InfrastructureMode functionality.