Database server vocabulary

Database server	Within ArcGIS software, the term database server refers to an instance of Microsoft SQL Server Express that has been enabled to store desktop or workgroup geodatabases.
Dbo	Dbo is a type of system user in SQL Server databases. Any login that is in the SQL Server fixed-server role sysadmin is a dbo. On database servers, all server administrators are members of the sysadmin fixed server role and are, therefore, dbo. All tables and feature classes created by server administrators are stored in the dbo schema in the database.
Desktop geodatabases	Geodatabases on a database server that are licensed through ArcGIS Desktop are referred to as desktop geodatabases. Desktop geodatabases can be accessed by a few users and edited by one user at a time
Geodatabase administrator	A geodatabase administrator is a Windows-authenticated user assigned to the SQL Server Express fixed-database role, db_owner. This user can perform administrative tasks in the geodatabase, such as administering other users' geodatabase permissions, making a backup of the geodatabase, and compressing the geodatabase.
Server administrator	A server administrator is a Windows-authenticated user who manages database servers. This user is dbo in the SQL Server Express instance and is responsible for the administration tasks on the database server. Every database server must have a server administrator. This user is added when the SQL Server Express instance is installed or enabled for geodatabase storage.
Windows authentication	Windows authentication is a method for identifying an individual user with credentials supplied by the Windows operating system of the user's computer. Database servers in ArcGIS always use Windows authentication.
Workgroup geodatabases	Geodatabases on a database server that are licensed through ArcGIS Server (Basic) Workgroup or ArcGIS Enterprise Workgroup are referred to as workgroup geodatabases. Workgroup geodatabases can be accessed by up to 10 users at a time, all of whom can be editing concurrently. You can also use web services and applications to access data in workgroup geodatabases.