Product Life Cycle
The product life cycle is the process of managing the entire lifecycle of a product.
Real Life Examples
A real life example may be the iPhone, many different iPhones, but all have similar purposes. The iPhone 4 would be decline, the iPhone 5c and 5s would be mature, the iPhone 6 and 6+ would be growth, and the apple watch would be introduction.
Extension Strategy is when a product is going through maturity and is soon to be on the decline, companies will try and make it so that product keeps selling.