Waterfall

A product methodology where the stages of the project happen in serial, one after the other. All the requirements are written, all the code is developed, and so on. Useful in fixed-bid projects. Trades predictability for flexibility.

Big downside is that there's no feedback loop with the customer until the very end of the project. See Agile for a different approach.

Spiral

Waterfall with multi-phase delivery, visualized as an outward-moving spiral.

V-shaped model

An SDLC model in which the process runs sequentially in a V shape. It's also called the verification in validation model. It is based on the assignment of a testing phase to each corresponding development stage. The next phase begins only after the previous phase is completed.