What is loose coupling?

The loose coupling concept has multiple dimensions. For instance -

1. Integration between two applications may be loosely coupled in time using message-oriented middleware - meaning the availability of one system does not affect the other.
2. Integration may be loosely coupled in format using middleware to perform data transformation - meaning differences in data models do not prevent integration.
3. The service interface is independent of the implementation - meaning applications can be built by composing one or more services without knowing the services' underlying implementation.