What is the smothered checkmate?

It's basically when a king is unable to escape a knight's check because he is hemmed in on all sides by his own pieces.  There are a number of threads on this so check them out for a few examples...

https://www.chess.com/forum/search?keyword=smothered+mate

The other interesting thing about a smothered checkmate is that it is usually preceded by a queen sacrifice, e.g.:

I missed an elementary checkmate in 7 here after 19...f6.

And here's the smothered mate eric0022 means:

The first one is not exactly a smothered mate (even though the idea is similar) since not all the adjacent squares of the Black king are occupied by friendly pieces. For this type, we call it suffocation mate. 

one of my favorite mates is the smothered one