What is Waterfall Model

Waterfall Model is the Sequential model.In this model output of one phase becomes input of next phase.The review meeting is held before moving to next phase.There is no overlapping.Testing is done only after coding phase is finished.
The different phases are as follows:
1.Requirement Analysis:
All the requirements are collected and analyzed in this phase and then documented in SRS.
2 Design;
After the requirements are analyzed design is prepared  in this phase.The High level design and Low level design documents are prepared.
3.Coding:
Each unit is developed and later on integrated to develop a system.
4.Testing:
Once the coding is finished in this phase we perform the testing activity.Different  kinds of testing are performed as specified in  the scope of Test Plan.
5.Deployment:
In this phase the product is deployed in client location.
6.Maintenance:
In this phase the issues related with client environment are handled.It may include small changes the client wants.