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.
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