Essential database server vocabulary

Database server	Within ArcGIS software, the term database servers refers to instances of Microsoft SQL Server Express that have been enabled to store desktop or workgroup geodatabases.
Desktop geodatabases	Geodatabases on a database server that are licensed through ArcGIS for Desktop are referred to as desktop geodatabases. Desktop geodatabases can be accessed by a few users and edited by one user at a time
Workgroup geodatabases	Geodatabases on a database server that are licensed through ArcGIS for Server 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.
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. See The administrative user for database servers for more information.
Dbo	This 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.
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.
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.
ArcSDE geodatabases for SQL Server Express	In some Esri documentation, this term is used along with the name of the software it is licensed with, to refer to workgroup and desktop geodatabases. For example, an ArcSDE geodatabase licensed through ArcGIS for Desktop is a desktop geodatabase.