What the heck is a host key and how do I use it?

I was in a meeting, basic version, one night before the person who is the host for that meeting had arrived.  We were attempting to get the HOST TOOLS up and running without him.  One woman said we had the HOST KEY.  Catch wass none of us knew what host key is, we sure we didn’t have time to practice so we did not use it.  We had concerns that we could crash the meeting while trying it out.  I would love to hear answers before Monday (tomorrow) at 16:00 so I have4 time to practice and use it in that night’s meeting.  THANK YOU!