The difference between an access point and a bridge

What is the difference between an access point and a bridge?
MAC bridges relay Layer 2 frames between LANs. An Ethernet bridge relays frames between two 802.3 LANs, while a wireless bridge relays frames between an 802.11 WLAN and an 802.3 LAN.

Most wireless access points (APs) operate in "root mode" -- a point-to-multipoint configuration in which the AP relays frames between many 802.11 stations and an adjacent Ethernet LAN.

Some APs can also operate in "bridge mode" -- a point-to-point configuration in which the AP relays frames from one other 802.11 bridge onto an adjacent Ethernet LAN.

Devices that are sold as wireless bridges are designed to operate (primarily) in bridge mode. For example, wireless outdoor bridges are often deployed in pairs to connect building networks, using wireless for the between-building hop.

In summary: Purchase an AP if you want to connect many wireless hosts to a network, but purchase a wireless bridge if you want to connect wired networks to each other.