An app is the common slang term for a software application or software program that can be run on a computer device to accomplish a task; namely, to accomplish it easier and more efficiently than we could do it ourselves as mere mortals.
If you have a smartphone or computer tablet, you probably have used some game apps, news apps, or even map apps to help you find the local coffee shop.Application development is the name of the profession that employs people who design, develop, and deploy these computer applications.
The steps included in a systems lifecycle for developing a computer application are:
Planning which involves identifying a need, consideration of solution options, and possibly considering the features of competing applications.
Analysis which involves documenting the functional requirements for the app and anticipating potential problems that may be encountered.
Design which involves defining how the app will work and what features and components it will have.
Construction which is where the actual programming occurs using the requirements and design as a guideline.
Testing which involves trying out the app looking for errors and confirming that documented requirements are met.
Implementation which involves making the app available for people to use.
Support which involves monitoring the user experience. Sometimes recommendations for revisions arise. If those recommendations are pursued, they'll go through the lifecycle also.