Instance

In short: An instance is a concrete specimen of something that was created from a template and currently exists or runs.

In more detail: The term is used in several places, always with the same idea: there is a template (class, image, program) and any number of running executions of it.

In Depth

• Programming: an object is an instance of a class. The class “Car” is the blueprint, a single car with a colour and licence plate is an instance. Creating it is called instantiating.
• Servers and cloud: an instance is a running server or virtual machine that was started from an image. Several identical instances can be started to spread load.
• Databases: a database instance is a running database process with its data, on which several databases can live.
• Applications: “An instance of the program is already open” means it is already running once.
• To remember: template = class/image, instance = the specimen that is actually there.

See also: instantiating, cloud, Docker