What does it mean when a position is "complicated"? I have watched many of GM Daniel King's videos where he analyzes games. He is always saying "the position is complicated" or "the position is fantastically complicated".

But what does this mean?

If I, eg, put such positions into a chess engine (such as Stockfish) how do I see the complexity factor?  Normally all I see is a simple +.nn number that completely characterizes the best next move.
Well, according to Merriam Webster:


  difficult to analyze, understand, or explain 


Unfortunately, you have to trust the GM on this (unless you are a strong player yourself). There is no way of using a chess engine to determine this. What is complicated for a human (positions with a lot of tactics, with a lot of possible capture sequences) might be very easy for a computer, and complicated positions for a computer (strategic battles) might be a lot easier for humans to judge.