What is mean by 'server','instance' in MSSQLServer 2005

Question

IN MS SQLSERVER 2005 I cannot understand the following terms

server

instance

Answer 1

A server is a (physical or virtual) machine hosting SQL Server software.

An instance is a collection of SQL Server databases run by a single SQL Server service, ahem, instance. You can view each separate instance you're running in your service console. Each instance can be started or stopped individually.

You're meant to use instances to partition data and policies. Each instance has completely separate databases, connection configuration, and security credentials.

Answer 2

If there are multiple server installations on single machine they are identified by instance name. In your connection string use format {server}\{instance} for non-default instances.