You can add tooltips to any word, such as an acronym or specialized term. Tooltips work well for glossary definitions, because you don't have to keep repeating the definition, nor do you assume the reader already knows the word's meaning.
Creating tooltips
Because this theme is built on Bootstrap, you can simply use a specific attribute on an element to insert a tooltip.
Suppose you have a glossary.yml file inside your _data folder. You could pull in that glossary definition like this:
<a href="#" data-toggle="tooltip" data-original-title="{{site.data.glossary.jekyll_platform}}">Jekyll</a> is my favorite tool for building websites.</a>
This renders to the following:
Jekyll is my favorite tool for building websites.