Truth
Fact, Reality
noun
The action of truth is just truth itself, though it's also facts and reality as well. Really, it's the idea of "truth" in a way.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.
以上は、全て事実です。
All of the above is true.
この本には、数学にまつわる事実がたくさんのってます。
This book has many facts about mathematics.
全日本の人々が知っている事実だが、北海道のカニはおいしい。
It's a fact that all Japanese people know, but crabs in Hokkaido are delicious.