The YubiKey is a hardware authentication device manufactured by Yubico. It is a write only device that is meant to hold various authentication keys. The fact that it is write only means that people can't duplicate these keys. Noah Chelliah from Altispeed says that he uses YubiKeys at his company so that when employees moves on from his company he only needs to take their YubiKey.
Now I don't manage any infrastructure larger than a couple computers, so why are these things interesting from a home use perspective? Well it allows you to have two-factor authentication separate from your smart phone. I was never a large fan of using my cell phone for two factor since you usually change cell phones every couple years.
What I wanted to highlight is how easy it is to integrate it with Linux. The Pluggable Authentication Module (PAM) is responsible for authentication and other various utilities in Linux. By adding a couple of lines to a couple of text files, you can add two-factor authentication to your laptop!
Instead of rewriting a bunch of instructions I got from somewhere else, I'll direct you to Yubico's own documentation entry. Happy hacking!