Jigsaw is the Java standard module system released with JDK 9. The whole JDK 9 is reorganized with Jigsaw. That means after JDK 9, you will not find the huge “rt.jar” file in the JDK directory, instead a “$JDK_PATH/jmods” directory full of “*.jmob” files is introduced and all the files in it are the module files.
Another interesting post here compares Jigsaw and OSGi.
And don’t forget the official site of Jigsaw here which lists several good Youtube videos about Jigsaw.