A service set identifier (SSID) is a code attached to all packets on a wireless network to identify each packet as part of that network. The code consists of a maximum of 32 alphanumeric characters. All wireless devices attempting to communicate with each other must share the same SSID.

There are two major variants of the SSID. Ad-hoc wireless networks that consist of client machines without an access point use the BSSID (Basic Service Set Identifier); whereas on an infrastructure network which includes an access point, the ESSID (E for Extended) is used instead. Each of these different types may be referred to in general terms as SSID. A network's SSID is often referred to as the "network name".

The most basic form of wireless network security is to turn off the broadcast of the SSID, and to the average user there does not appear to be a network in use. However this should not be the only form of defence to protect a wireless network. Other forms of encryption and authentication should also be used.