Availability – The capability of a system to continue working despite faults and/or failures.

Buffer Pool (aka Data Cache) (SQL Server) – A region of memory used to cache the contents of data files.

Data File (SQL Server) – A file in the file system that contains the physical data records and structure of a database.

Deadlock – A state where two or more processes are both holding and requesting resources such that none of the processes can proceed further.

Extent (SQL Server database engine) – A logical container of 8 pages (for a total of 64 KB).

Failover – The process by which a service is returned to an available state using alternative resources.

Filegroup – A logical container of data files.

Guard Condition – A programming technique where a logical test is designed such that a main block of code below does not execute under certain circumstances. When the test condition is met, usually either an error is raised, or a trivial function result is returned immediately without the need for further processing. The condition “guards” the code below by rejecting unwanted or unhandled use cases.

Job (SQL Agent) – A predefined set of ordered actions. A job can be executed manually, on a schedule, or in response to selected server events.

Linked Server – An instance-level object that allows users to run queries on an external server.

OLTP (Online Transaction Processing) – A database system design that favours usage by applications; generally characterized by small, short transactions, and fast query response times.

Log File (SQL Server) – A file in the file system that contains a record of the physical operations needed to perform (do) and revert (undo) changes in a database.

Page (SQL Server database engine) – An 8 KB (8,192 byte) region of storage.

Recovery Model – A database configuration setting that controls how SQL Server records and retains information about transactions that occur. The recovery model determines which types of restores are possible for that database. The three recovery models currently supported in SQL Server are SIMPLE, BULK_LOGGED, and FULL.

Replication – A process by which data is duplicated from one system to another.

Scalability – The efficiency of a system’s output for different volumes of input; the capability of a system to handle an increased demand or load.

Service Level Agreement (SLA) – A mutual understanding or contract for a service to operate within certain requirements. For example, an availability SLA might specify that the service must be available 99.99% of the time during business hours, 7 days/week.