Waterfall
A linear project management approach where stakeholder requirements are gathered at the beginning of the project, and then a sequential project plan is created to accommodate those requirements.
Impact
Waterfall assumes you know everything at the start. In software, this is rarely true.
Weinto take
Waterfall is for construction, not code. If you are building a bridge, use Waterfall (physics doesn't change). If you are building software, use Agile (requirements change). Don't mix the paradigms.