A Fast IDentity Online (FIDO) device is a hardware authentication device used to protect access to computers, networks, and online systems that support one-time passwords, public-key cryptography, and authentication.
Typically, you either insert the FIDO device into your device or wirelessly connect it, then press a button on the device itself. The FIDO device cryptographically signs a challenge by the web browser, verifying your identity and granting access.
You can use a FIDO device to authenticate into almost any system, but it's recommended to use a dedicated one for the Internet Identity and authorize as many other devices as possible.
Ideally, you’ll want to purchase a device that supports FIDO U2F and can communicate with both your phone and your computer.
Updated