I once read of a python library for creating a certain type of
cryptography.  I've forgotten the keyword for this kind of crypto and
so I can't find it!

What I'm talking about:  You encrypt a file, and generate three keys,
and give a key to each of three people.  No single key can open the
file.  It requires *any two* of the three keys to open it.

What's the term for this?  Not "federated?"  Is "escrow" in there
somewhere?  Can one of you crypto-spook types help me name what I'm
looking for?