Final answer:
A key is considered a physical token, which is part of 'something you have' category, one of the three types of authentication factors. It is used in physical security and can be part of a multi-factor authentication strategy.
Step-by-step explanation:
A key would be described as a physical token in the context of authentication factors. Authentication factors are typically categorized into three types: something you know (like a password), something you have (like a key or security token), and something you are (like a fingerprint). A key, being a physical object, falls under the category of “something you have” and represents a form of physical security.
When it comes to securing data or access to a system, utilizing multiple types of authentication factors can greatly enhance security. This strategy is known as multi-factor authentication (MFA), which often combines two or more different types of credentials to verify a user's identity. For instance, accessing a secured facility might require both a key card (physical token) and a password or PIN (knowledge factor).