It describes the processes of planning, creating, testing and deploying an application.
The actual coding that people are familiar with is simply one part of a broader 'life cycle' which sees the application all the way through from idea to eventual retirement.
This consists of basic questions such as who will use it, what data it will require and provide.
However, the software cannot be deployed immediately; it then has to be extensively tested to see if it is meeting the key requirements as detailed in the earlier phases.
Finally deployment comes, usually through beta testing, where the initial users can report bugs to the developer team.
The final stage is maintenance, where the experience of the actual users of the software, including problems and errors encountered, is fed back into the application to continuously improve it.