What is the difference between content type and content entity?
Content Types are one of the main building blocks within a Drupal site; as the name suggests, content types hold content. However, different content types can hold different kinds of content; an event can hold information that is specific to a time, where a discussion can be used for people to talk. Most sites have multiple different content types, and the name of a content type will ideally give information about how it is used.
An Entity is a piece of data within a Drupal site. Nodes, users, comments, and taxonomy are all entities; additionally, with custom code, you can create new entity types if/when needed. You can also add fields to entities, which allows for things like detailed user profiles, or more sophisticated comment forms.