Almost all websites have one requirement in common: getting notified when something specific is happening. Whether that's a new blog post, a new comment, a modified version of a node, an exception in the logs or a deleted user account, either the site admin or website visitors would like to know about some or all of these.
The Drupal 8 module Onomasticon automatically displays the definition of taxonomy terms everywhere a term is used. However, you may want to avoid self-definition on the term's own page as its description is already visible without it.
module for adding and editing abbreviations in Wysiwyg CKEditor.
The User hash module allows you to create an individual hash for each user. Use it as a light-weight user identification where you do not want to use the login credentials. E.g. as an individual API Key for reading insensitive content.