https://www.cisco.com/c/en/us/td/docs/security/ise/2-1/admin_guide/b_ise_admin_guide_21/b_ise_admin_guide_20_chapter_010110.html Posture is a service in Cisco Identity Services Engine (Cisco ISE) that allows you to check the state, also known as posture, of all the endpoints that are connecting to a network for compliance with corporate security policies. This allows you to control clients to access protected areas of a network.

Reference:
https://www.cisco.com/en/US/docs/security/ise/1.0/user_guide/ise10_man_id_stores.html

Reference:
If you do not have a matching profiling policy, you can assign an unknown profiling policy. The endpoint is therefore profiled as Unknown. The endpoint that does not match any profile is grouped within the Unknown identity group. The endpoint profiled to the Unknown profile requires that you create a profile with an attribute or a set of attributes collected for that endpoint.
https://www.cisco.com/en/US/docs/security/ise/1.0/user_guide/ise10_man_identities.html

Section: Web Auth and Guest Services