Linear economy:  This the apparently easy way to use stuff.  It is very convenient for the current consumer but bad for future generations.  In this system, raw material (e.g. iron ore) comes from some source, gets processed, made into something that you buy, use and then dump to landfill.  This system seems cheaper than the linear economy, but that is because the cost of the initial (almost always finite) resource is not included, nor the impacts of ever increasing numbers of landfills scattered around the countryside, with the issue they contain, such as leaking methane emissions.

Circular economy:   This is the virtuous way to use, and reuse stuff.  In this system, some raw product (as little as possible) is mined, but most of the product comes from the old stuff in an endless cycle, for example:  Milk in milk bottle:  bottle emptied, cleaned:  sent to recycling plant, broken down/chopped up and used as raw material for a new milk bottle which is filled with milk and sold again thereby repeating the cycle, again and again and again.