Final answer:
A Service Principal is an identity used by a service or application in Azure Active Directory (Azure AD) to authenticate and access resources. MFA and SSO are authentication mechanisms that can be used alongside Service Principals, but they are not identities themselves.
Step-by-step explanation:
An identity that is used by a service or application is known as a Service Principal. A Service Principal is an identity in Azure Active Directory (Azure AD) that represents an application or service and allows it to authenticate and access Azure resources.
Multi-Factor Authentication (MFA) and Single Sign-On (SSO) are authentication mechanisms that can be used alongside Service Principals, but they are not identities themselves. MFA adds an extra layer of security by requiring multiple forms of verification, such as a password and a mobile device. SSO allows users to log in once and access multiple applications without having to provide credentials for each one.
Therefore, the correct answer to this question is A) Service Principals, as MFA and SSO are not identities, but rather authentication methods.