Well, the term “models” comes up a lot in software development in a variety of different contexts.

The ones you mention are specifically to do with what’s commonly called the software development “life cycle”. As the name suggests, that refers to the process used to create a piece of software over time – in what order and in what way it’s specified, designed, built, tested, maintained, so on. “Models” in this context are a particular overall structure for that life cycle, given a descriptive name. E.g. as the name “waterfall” might suggest, under that particular model you move through a set of steps in a linear sequence.

  

 Next Topic: Software TestingLife Cycle (STLC)