- SSID — The wireless network “display” name.
- BSSID — The MAC address of the access point currently being used.
- ESSID — A collection of BSSIDs representing a single network. More-or-less analogous to SSID (when used in the context of networks consisting of multiple access points).
From what I can tell, SSID and BSSID apply to single access points, while ESSID applies to an entire network of access points.