Are native in the EJS library. (unlike layout) Are used for static or reusable pieces of text such as nav bars or footers.

"Partials provide easy maintenance of your code. For example, if you create navigation on all of your pages, when you need to add a new entry to the navigation, you must then update every single page with this change.

The navigation partial will be inserted into every page that requires it. To add a new entry to the navigation, you need to just update the partial and it will automatically be applied to every page that contains the nav partial." used from How to use EJS Templating in a Node.js Application on (free code camp)

In EJS, any JavaScript or non-HTML syntax you include in your templates is always surrounded by <% %> delimiters.