What is a YubiKey and Why I might need one?

Yubikey's and other smart devices are used to help login to secure systems and they dont have access to a phone and an authenticator app.

A YubiKey is a small hardware device that provides strong, phishing-resistant multi-factor authentication for online accounts, apps, and systems

 Examples Only   

I might need one if I am not able to use Passkey with my Phone to Authenticate/Login.  Some people might need one for backup authentication.