A company that operates oil/gas rigs in the Permian Basin (upstream) buys an LNG and Oil export terminal in Houston (midsteam), and merges with a gas station company (downstream.
A Car Manufacturer like GM buys an OEM (original equiment manufacturer) and a car dealership.
You can self learn here. There is tons of literature on this on investopedia & youtube.
It means a company buys another business up or down the value chain. E.g. A suger refinery buying the sugar cane farms to secure long-term supply (up), or a chocolate factory (down).
