I've been reading and enjoying the site immensely.
What is the "Endgame Tablebase"? I see it referenced frequently.
Endgame tablebases are essentially databases containing known endgame positions that have been “solved”, so to speak. That is, every position in an endgame tablebase will have a corresponding result which will either be a win for white, a win for black, or a draw (assuming perfect play). They are used by chess engines because it is much more efficient for the computer to look up an endgame position in a database to get the result of the endgame rather than exhausting all the possible variations to determine the result.
Endgame table base is a huge tree of information, which solves the game of chess, with minimum number of pieces. We have reached up to 7 pieces up till now and the best quality tablebase is maintained by Ronald de Man at syzygy endgame tables
Basically, Endgame Tablebases are a collection of positions involving a number of pieces, with optimal moves in the situation provided(e.g., In a Q+KvK endgame, the longest checkmate is mate in 9.)
Tablebases are used to save a chess engine's memory. It is easier to simply search up an optimal line instead of calculating all possible positions.
However, at this time, tablebases are still very limited, and the largest we have are 7-man tablebases.