Yubico FIDO U2F Security Key is a USB device that uses the FIDO U2F protocol. It will work with websites that support the FIDO U2F protocol like Facebook, Google, Google Apps, GitHub, BitBucket, and Dropbox.

FIDO Alliance, or just FIDO, in short, is an open authentication industry consortium.

Yubico FIDO U2F Security Key - Packaging Front
Yubico FIDO U2F Security Key – Packaging Front