Waterfall model:
                 It is SDLC Model which is used for testing 
projects.Since it is a simple and elegant model which can 
be used widely in testing projects

Muralidharan

dharanmu@yahoo.com

It is one of the software development model, if at all the 
custemer requirements are very clear then that situation we 
can use this model.

the waterfall model is a sequentially software development 
model in which the development is seen as flowing steadily 
downwards(like waterfall) through several phases.

waterfall model is very simple and basic model for developing 
other models.hence it is said to be a classic life cycle model

Adding to the above answers with more precisely, 

In a typical model, a project begins with feasibility 
analysis. On successfully demonstrating the feasibility of 
a project, the requirements analysis and project planning 
begins.  The design starts after the requirements analysis 
is complete, and coding begins after the design is 
complete.  Once the programming is completed, the code is 
integrated and testing is done. On successful completion of 
testing, the system is installed.  After this, the regular 
operation and maintenance of the system takes place.

Please let me known if you need flow chart which i prepared 
for the above explination.

Thx,
sudir
sudir.csc@gmail.com