A Simplified Lifecycle
Most projects in most organisations will go through a series of phases. You may have more, or fewer. For example:
Initiation, Feasibility (which can include trade-offs between different possible solutions), High level design, Detailed design, Build and test, Deploy or launch, Evaluation
Between these phases there will be milestones, such as Kick-Off, Preliminary and Critical design reviews, Test & Validation reviews, Sprint planning meetings and Sprint reviews
And in addition there may be higher level program or portfolio reviews.