Implementing a Firewall Services Module (FWSM) in a Virtualized Network
A context on a Firewall Services Module (FWSM) is analogous to a virtual machine in VMware or to a switch that supports multiple VLANs. Although you are using the same physical hardware, you can logically separate the firewall functionality into unique instances. This is also known as virtualization. Each context has a unique set of interfaces, rules, and/or policies applied.
Rather than install a new firewall every time a new customer, department, agency, application, and so on is added, creating a new context is very simple and does not require any additional rack space. The footprint of a device is a huge concern in locations where customers lease space by the Rack Unit (RU). Multiple contexts do not require additional space. The "green" initiative is concerned with the impact on our environment. Reducing the amount of power consumed by leveraging multiple contexts and consequently reducing the hardware will help us do our part in being ecologically responsible.
Thought I'd throw in a Cisco tutorial in the News just to liven things up. See the rest at Cisco.com.