H2 is a relational database management system written in Java. It can be embedded in Java applications or run in the client-server mode.
This database is the default solution embedded in Talend Administration Center to store all cross-project information such as users, authorizations, projects...
If you do not want to use this default database, you can set up a database server (MySQL, MSSQL or Oracle).
The benefits of using this H2 embedded database is that it simplifies the installation process.