Ahh, JQuery one of the most used and most useful libraries in the WordPress ecosystem. It would be quiet difficult to imagine WordPress without JQuery. That being said, WordPress doesn’t use the latest version of JQuery and this can be both a good and bad thing.
JQuery is basically a JS library that makes it easier to do other things with JS (very high-level sentence there). But on a more serious note, WordPress by default does not include the latest version of JQuery and there are in fact there are three branches of JQuery core.
There is the branch WordPress uses the 1.x branch (1.12.4 is the latest and shipped in core), the 2.x branch and the 3.x branch.
Enter JQuery Updater
However, on incredibly simple sites with basic theme installs like 2017, it actually managed to work (for the most part). There was some performance benefit gained by swapping to the newer version too. Not enough to make 29% of the internet swap to it in an update, but there was some gain.
However, if you like to be on the bleeding edge or want to test your theme/plugin in a WordPress environment JQuery Update makes this process as simple as activating a plugin.