What is gssapi-with-mic?

Debugging a Nagios warning on ssh, I've discovered that gssapi-with-mic is causing long lags in authentication. I've turned it off, but what exactly am I missing? I gather that GSSAPI is a tool for authentication, but what about the -with-mic part?

Message Integrity Code.

This is also called a Message Authentication Code, but that acronym gets used for other things, so MIC is less ambiguous. From that Wikipedia page:

The term message integrity code (MIC) is frequently substituted for the term MAC, especially in communications, where the acronym MAC traditionally stands for Media Access Control.

The fix is simple: disable attempts to use GSS-API by adding the following to ~/.ssh/config:

GSSAPIAuthentication no