Elementor is a visual page builder plugin for WordPress enabling the creation of web pages in a live, visual way. It replaces the basic WordPress editor with a live frontend editor, so you can create complex layouts visually, and design your website live, without having to switch between the editor and the preview mode.
A free version of the Elementor is bundled and required for Jupiter X.
If you want to use the Elementor Pro, it needs to be purchased separately. But it's not necessary as Jupiter X provides exclusive Raven plugin that has great capabilities extending Elementor power even more. It has additional widgets that will be helpful when building a website. Read more about Raven plugin in this article.
Also there is other premium plugin bundled in the theme exclusively built to enrich the Elementor plugin - JetElements plugin.
Jupiter X offers some features that do not exist in Elementor Pro and the opposite is also true meaning that Elementor Pro may have some features that are not available in Jupiter X.