I think they're engines for endgames or something like that. They calculate everything and can tell you for certain if it's a win, loss or draw.
Tablebase?

They show perfect play in positions with up to 7 pieces (kings included). They're useful to test your analysis in some cases, but I wouldn't call them "vital for chess improvement" by any means.
https://en.wikipedia.org/wiki/Endgame_tablebase

yup, so there are different tablebases (like 3 piece tablebases, all the way up to 7 piece tablebases). Any chess position with 7 or less pieces on the board had been calculated by computers all the way to game termination. http://chessok.com/?page_id=361 is one example of a tablebase. put in a position with 7 or less pieces and it should say something like "draw" or "mate in 368" or something like that.
That is so cool! I went to the website and tried a few positions. Will they ever have 8 piece tablebases?

Note that tablebases are not a permitted resource in daily chess. You can, of course, use them for post-game analysis, or for studying endgames that are not relevant to a current ongoing game. And of course, in unrated games where both players agree, you can have whatever rules you want.

And of course, in unrated games where both players agree, you can have whatever rules you want.
I didn't know that! Wow, I wonder how many people have agreed to copy some famous game.
I've heard of tablebases. I was reminded most recently in the news article about So winning the rapid portion of the GCT event in Leuven.
What exactly are tablebases, and are they necessarily that vital for chess improvement? Give me your thoughts. Thanks!