A linked server is a virtual server that has been defined to SQL Server with all the information needed to access an OLE DB data source.
A linked server name is defined using the sp_addlinkedserver system stored procedure. The linked server definition contains all the information needed to locate the OLE DB data source. Local SQL Server logins are then mapped to logins in the linked server using sp_addlinkedsrvlogin.
Remote tables can then be referenced by using the linked server name as the server name in a four-part name used as a table or view reference in a Transact-SQL statement. The other three parts of the name reference an object in the linked server that is exposed as a row set.
Remote tables can then be referenced by using the linked server as an input parameter to an OPENQUERY function. OPENQUERY sends the OLE DB provider a command to execute. The returned row set can then be used as a table or view reference in a Transact-SQL statement.
