The term 'Mountain Resource in Catan' can be summarized as ORE, which is a three letter word. ORE is a type of mineral or rock that contains valuable metals, such as iron, copper, and gold. It is a natural resource that is mined from the earth and used for various purposes, including manufacturing and construction. In the board game Catan, ORE is one of the resources that players can collect to build settlements and roads.