What I can recall from what I know about all types are:
- Waterfal model
- Spiral model
- Agile model
Most of the models I studied like one year ago for the first time, but I can describe them as an scheme what you follow when you are developing certain software project or just giving it maintenance, so you will be able to follow a protocol and as Mohamed defined it is a series of phases that provide a common understanding of the software building process and how it will be developed in the business understanding and requirements.