SSID - service set identifier
SSID is short for service set identifier.
SSID is a case sensitive, 32 alphanumeric character unique identifier attached to the header of packets sent over a wireless local-area network (WLAN) that acts as a password when a mobile device tries to connect to the basic service set (BSS) -- a component of the IEEE 802.11 WLAN architecture.
The SSID differentiates one WLAN from another, so all access points and all devices attempting to connect to a specific WLAN must use the same SSID to enable effective roaming. As part of the association process, a wireless network interface card (NIC) must have the same SSID as the access point or it will not be permitted to join the BSS.
SSID is also referred to as a network name because essentially it is a name that identifies a wireless network.
SSID is considered to be a fairly weak form of security because an SSID can be sniffed in plain text from a packet and most access points broadcast the SSID multiple times per second within the body of each beacon frame. A hacker can easily use an 802.11 analysis tool to identify the SSID. Some network administrators turn off SSID broadcasting, but a hacker can still sniff the SSID from frames that stations use when associating with an access point.
Using Multiple SSIDs
Using multiple SSIDs allows users to access different networks through a single access point. A network manager can assign different policies and functions for each SSID, increasing the flexibility and efficiency of the network infrastructure.