A claim, or attribute, could be almost anything that can be owned by, or associated with, an individual. It can be unique to that individual e.g. their email address, or can be a property that is shared by many others, such as a date of birth or gender.
Other examples of claims include membership of an organisation or group, qualifications, credit rating, etc.
Claim values may be entered by a user, at registration, or obtained in real time from a claims provider - a trusted external party or government organisation - or a local database or directory.
See also Verified Cloud Identities.