Direct Relationship: A direct relationship occurs when two variables move in the same direction; as one variable increases, so does the other.
Supply and Demand: Supply and demand are fundamental economic concepts that describe how prices are determined in markets. They often exhibit inverse relationships - when supply increases, prices tend to decrease, while increased demand leads to higher prices.
Opportunity Cost: Opportunity cost refers to what must be given up in order to obtain something else. It often involves making choices where there is an inverse relationship between the benefits of different options.