How to describe two knights defending each other? How to describe two knights defending each other?

Linked knights? 

Doubled knights?



In Chinese Chess, two 马 (horse/knight)s protecting one another is quite common, and there is a standard terminology: "连环马".



There is a real case: "German Chess Prodigy Surprises Boris Gelfand With A Brutal Queen Sacrifice"(https://www.youtube.com/watch?v=l37hlb32Rs0)
They're connected knights.

As the other answers said, this isn't typically that smart a thing for knights. OTOH, rooks are very often made stronger by connecting them (it allows them to thwart any queen intrusion). Thus you'll more often hear about it being “a good idea to connect rooks now”. But I think I've also heard the term used with knights. Just, knights tend to serve more of a tactical role than solid defense of the back-rank, and they're usually better protected by pawns or bishops, as these don't reduce their mobility in the way mutual knight defense does.

For pawns, the term connected of course means something different, since two pawns can never protect each other mutually.