Here is a list of all topics with brief descriptions:

[detail level 12]

API
Actions
BagOStuff
Change tagging	Tagging for revisions, log entries, or recent changes
CommentStore
Database	This group deals with database interface functions and query specifics/optimisations
Debug logging
DifferenceEngine
Dump
Entry points
ExtensionRegistry
ExternalStorage
Feed
▼File Repository
File abstraction
▼File backend
Lock management
▼Hooks	Hooks allow custom code to be executed when an event occurs; this module includes all hooks provided by MediaWiki Core; for more information, see https://www.mediawiki.org/wiki/Manual:Hooks
ResourceLoader Hooks
Installer	The Installer helps admins create or upgrade their wiki
▼Internationalisation
Languages
JobQueue
Mail
▼Maintenance
Benchmark
Maintenance archives
▼Media
Mime
Page
Pager
Parser
Profiler
Recent changes	Discovery and review of recent edits and log events on the wiki
▼ResourceLoader
ResourceLoader Hooks
Search
Skins
SpecialPage
Upload related
Users watchlist handling