TYPO3 v9 has reached its end-of-life September 30th, 2021 and is not maintained by the community anymore. Looking for a stable version? Use the version switch on the top left.
You can order Extended Long Term Support (ELTS) here: TYPO3 ELTS.
"User TSconfig" and "Page TSconfig" are very flexible concepts for adding fine-grained configuration to the backend of TYPO3 CMS. It is a text- based configuration system where you assign values to keyword strings, using the TypoScript syntax. The TSconfig Reference describes in detail how this works and what can be done with it.
User TSconfig can be set for each backend user and group. Configuration set for backend groups is inherited by the user who is a member of those groups. The available options typically cover user settings like those found in the User Settings, configuration of the "Admin Panel" (frontend), various backend tweaks (lock user to IP, show shortcut frame, may user clear all cache?, etc.) and backend module configuration (overriding any configuration set for backend modules in Page TSconfig).
Page TSconfig can be set for each page in the page tree. Pages inherit configuration from parent pages. The available options typically cover backend module configuration, which means that modules related to pages (typically those in the WEB main module) can be configured for different behaviours in different branches of the tree. It also includes configuration for the FormEngine (Forms to edit content in TYPO3) and the DataHandler (component that takes care of transforming and persisting data structures) behaviours. Again, the point is that the configuration is active for certain branches of the page tree which is very practical in projects running many sites in the same page tree.