Below is a brief description of each of the databases that ship with MarkLogic Server:

App-Services

contains data for the "Application Services" suite of apps that are available on port 8000 on installing the product. The database also contains executed "Query Console" history and "Workspace" metadata so queries and code written in the Query Console buffers is retained. (read more about the App-Services database)

Documents

A default database for documents (content loaded into MarkLogic Server); empty on first install

Extensions

Used for any installed MarkLogic Server Extensions (plugins); empty on first install (you can read more on plugins and view the API documentation)

Fab

Used to store state information for the "Information Studio" application that ships with MarkLogic Server; empty on first install (you can read more about this database in our documentation).  Note that the "Information Studio" application has been deprecated beginning in MarkLogic 8. 

Last-Login

Used to store metadata about the last user to have logged into an application server; not enabled on any application server by default and empty on first install (you can read more about monitoring user activity in our documentation)

Meters

Used to store historical performance information for a MarkLogic instance (you can read more about monitoring MarkLogic performance history in our documentation)

The other key ("auxiliary") databases include:

Modules

A default database for XQuery library and main module code; empty on first install (you can read more about the Modules database in our documentation)

Schemas

A default database for XML Schemas used for validating content loaded into MarkLogic Server; empty on first install (you can read more about the Schemas database in our documentation)

Security

Contains information for all users, roles and privileges that ship with MarkLogic Server; contains data on first install and is routinely updated in maintenance releases of the product (you can read more about the Security database in our documentation)

Triggers

Contains metadata for all configured database triggers; empty on first install (you can read more about the triggers database in our documentation)

We recommend regular backups for Security database and for Schemas, Modules and Triggers databases if they are actively used.