Integration and Testing: All the units developed in the implementation phase are integrated into a system after testing of each unit. Post integration the entire system is tested for any faults and failures.
Deployment of system: Once the functional and nonfunctional testing is done, the product is deployed in the customer environment or released into the market.
Maintenance: There are some issues which come up in the client environment. To fix those issues patches are released. Also to enhance the product some better versions are released. Maintenance is done to deliver these changes in the customer environment.
Spiral model is a combination of iterative development process model and sequential linear development model i.e. waterfall model with very high emphasis on risk analysis. It allows for incremental releases of the product, or incremental refinement through each iteration around the spiral.
The spiral model combines the idea of iterative development with the systematic, controlled aspects of the waterfall model.
The spiral model has four phases. A software project repeatedly passes through these phases in iterations called Spirals.