Definition: authentication is the process of obtaining credentials, and as needed, additional tokens, to determine if a person is who she says she is.
IAM provides CAS and Shibboleth authentication services. CAS services are generally used for locally developed and hosted web applications; Shib authentication services are generally used for 3rd party applications (e.g. Google@UH and Cyber Infrastructure for research). With each successful authentication a standard set of person attributes is returned to the application. These attributes include name and contact information, as well as roles and campus affiliation information.
Developer resources, further reading: