Waterfall

In software: progress flows in largely one direction (“downwards” like a waterfall) through the phases of conception, initiation, analysis, design, construction, testing, deployment and maintenance.
In general: a Waterfall process is any process with well-defined, sequential steps, with no going back to ‘correct’ a previous step.
Any amount of going back to ‘correct’ previous work is introducing agility into the process, so few actual processes are strictly Waterfall.