CMS - Content Management System

TYPO3 is a content management system, also called CMS for short. It is mainly used to display content (text and media).

As an enterprise content management system, TYPO3 supports multiple users in a collaborative environment and digital asset management.

Separation of content and presentation

Separation of content and presentation is the separation of concerns design principle as applied to the authoring and presentation of content.

https://en.wikipedia.org/wiki/Separation_of_content_and_presentation

In TYPO3 the content in its raw form is edited in the backend, while the presentation is achieved in the frontend:

Backend and frontend of TYPO3 as an illustration

Backend and frontend of TYPO3 as an illustration

In the backend, for example, you can state that a headline should have level 2. This would be a content decision. However, in the frontend this headline is displayed in red and underlined. This is one example of what the presentation does.

The presentation is influenced by the sitepackage that your integrator or developer configured.