A wireless bridge connects two LAN segments with a wireless link. The two segments are in the same subnet and look like two Ethernet switches connected by a cable to all computers on the subnet. Since the computers are on the same subnet, broadcasts reach all machines. DHCP clients in one segment can get their addresses from a DHCP server in the other segment.Use a wireless bridge to transparently connect computers in one room to computers in a different room when you cannot—or don’t want to—run an Ethernet cable between the two rooms.A standard wireless bridge (Client Bridge) connects wired clients to a secondary router as if they were connected to your main router with a cable. Secondary clients share the bandwidth of a wireless connection back to your main router. Of course, you can still connect clients to your main router using either a cable connection or a wireless connection.

Source: Repeater Bridge – DD-WRT Wiki