The admin context is just like any other context, except that when a user logs in to the admin context, then that user has system administrator rights and can access the system and all other contexts. The admin context is not restricted in any way, and can be used as a regular context. However, because logging into the admin context grants you administrator privileges over all contexts, you might need to restrict access to the admin context to appropriate users. The admin context must reside on Flash memory, and not remotely.

Refer the following url for more info on configuring security contexts:

http://www.cisco.com/en/US/docs/security/fwsm/fwsm32/asdm52f/user/guide/contexts.html#wp1204601