Product Life Cycle
All products go through a product life cycle. A product life cycle is kind of like a normal life, product life cycle is Introduction, Growth, Maturity and Decline (you're born, you grow, you mature and then you die)
This is where the product is first introduced and people will have only just heard of it, like when the Xbox one was introduced, no one had ever heard of it before and it was new to everyone.
This is where the product starts to grow, so more and more people are buying it so that company is bringing in money.
When the product has reached as much sales as it can and a lot of people are buying it but not as many people as before.
This is probably the worst part for the company who created them, the item will have stopped selling and no one buys anymore (or very little people buy it) and the product sales just go down and down until no one buys it anymore.
What is Extension Strategy?
An extension strategy is a thing used to increase the market share for a given product or service and keep it in the maturity phase of the marketing product lifecycle other than going into decline.