Sitecore Content Databases are Master, Web, and Core.
These databases are most important for content management in Sitecore, so it is necessary to understand each of these databases.
Master Database
Master Database is managed by the Developers. It is the default database used by Sitecore Content Editor. It contains all the versions of all items created in Sitecore. All the templates, content items, layouts, settings, models, rendering, media library items, etc. are stored in the master database. All item number versions and language variations are also stored here. It also contains all the published and unpublished content.
Web Database
Web Database is used to support live websites. It is a subset of the master database which is optimized for size and speed over the master database. When content is published from Sitecore then it goes through the publishing task of workflow and the latest content version is copied from the master to web database. Whenever we want to make any changes on the website to go live then we have to move it to the web database from the master database. All the published content is stored in the web database. It does not contain any unpublished content. This database also includes one version for each language variation and number version. It is suggested not to edit anything in the web database directly as it will affect the live site and may lead to errors.
Core Database
Core Database contains core information required for running the Sitecore environment. It contains all Sitecore settings as well as the tables containing the .NET membership provider for authenticity and security (i.e. users and roles available in the Sitecore Instance). It also includes Sitecore user interface definitions (i.e. Content Editor, Experience Editor, etc.), application information, user preferences, and many other Sitecore settings.
References
Working with Sitecore Databases - https://doc.sitecore.com/xp/en/developers/92/sitecore-experience-manager/working-with-sitecore-databases.html
Defining relationship between Sitecore Databases - https://www.altudo.co/resources/blogs/defining-relationship-between-sitecore-databases
That's all for Today...