Requirement management: You probably have a very good idea of what this phase entails, as per Chapter 2, Software Requirements – Collecting, Documenting, Managing. In the Waterfall model, the requirement specification must be completed and formally accepted before proceeding with the next phase, while we discussed how, usually, an iterative approach is more natural.

Analysis/design: Sometimes defined as two different phases, the goal is to start from system requirements and then define the solution architecture to satisfy them. As in the previous phases, whoever is in charge of the next phase must formally accept the deliverables coming from this phase (such as system blueprints, diagrams, and pseudocode) in order for the process to continue. This basically means that developers must clearly understand what they are supposed to implement.

Implementation: In this phase, the development team, starting from requirements and from the deliverables produced in the previous phase, must write the code to implement a proper software solution. This phase is, of course, crucial, and the correct completion of this phase basically means the success of the whole project.

Testing: As seen before, the acceptance of the deliverables coming from the preceding step is part of each phase. With testing, the approval is so important (and so complex) that it overlaps with the whole phase. The Waterfall model does not specifically distinguish between different kinds of testing, but this phase is commonly intended as user acceptance testing.

Operations/maintenance: This is the final step, facilitated by technical activities ensuring the proper setup of the solution in a production environment, as well as all the planned and unplanned activities to keep it operating properly.