Any product goes through a life-cycle similar to living things. For example a butterfly, which starts life as an egg, hatches as a caterpillar, then becomes a pupa, and finally comes out as a flying creature to mate and die.In the field of engineering, the same term is used to denote the sequence of phases through which any product passes. In general, these stages can be listed as follows.

🔥Concept and feasibility study: Someone has a good idea, but will it work?

🔥Requirements definition: They find out that it can be done and decide to go ahead. Now they must define what exactly the product will do, and the level of quality needed for it to be viable.

🔥High level design: What are the main elements or subsystems of the product? How is each element required to function so as to meet the overall product requirement? What quality is needed in each element as to meet the quality requirements of the overall product?

🔥Low level design: Each main element is broken down into its basic components. Their functional requirements and quality requirements are also defined relative to the requirements for the element or subsystem. Depending on the size and complexity of the product being designed, there may be many levels of design. The process of breaking a complex system down progressively into smaller chunks is referred to as hierarchical decomposition.

 At the lowest level of design, the specified components are simple enough to be manufactured or bought in from an outside supplier without further design work.

🔥Construct and test a prototype. Proto is a prefix taken from the Greek, meaning "sole" or "only". Initially, only a very few (and sometimes only one) examples of a new design are constructed. These early constructed designs are called “prototypes”. These prototypes are tested, and any faults discovered in them are corrected before production begins.

🔥Manufacture: Many copies (also referred to as "examples", or "serials", since each one usually has a "serial number") are produced and sold. The total sales revenue obtained must cover both the cost of manufacture and the cost of the preceding design process for the manufacturer to make a profit.

🔥Maintenance: As nothing lasts forever, hardware wears out and must be replaced. The manufacturer will set up a maintenance operation so that customers can have their machines repaired. Sometimes design faults will be discovered after a product has been on sale for a while. It is then necessary to correct the design for later releases and in the worst cases (where the design fault makes the product dangerous, for example) it is necessary to recall the samples already sold.

🔥Obsolescence and decommissioning: Eventually it will be decided that the present model is no longer useful or successful, and the whole life cycle is repeated for a new, improved, design.

It is clear to see that the above life-cycle describes quite well what happens when a new car is designed and manufactured though the actual sequence of events may vary. A life-cycle should be regarded as a conceptual model of the process of development and manufacturing, rather than a fixed sequence of events that must be followed. It is an abstraction of the real process, and is useful as a tool for reasoning, in order to plan, estimate resources, and measure the progress.