Water leak on intake manifold

My 2003 tundra 4.7 4x4 had this plug popped out. It ran out of water and ran hot. I found it popped out while I was looking for the water leak.
I tapped it back into place. What is it? A freeze plug? How do I properly reinstall it?
thanks for the help.

 

I couldn't really find anything searching on this forum, but i found some info in these posts on tundra solutions: and an interesting post about someone who tapped the hole and filled it with a 3/8 npt plug and loc-tite'd it. . Someone had mentioned it was a hole created to machine the coolant passages. interesting.

 

That's exactly what I needed. Thanks Pnwtundy!

 

No problem!