A more thorough explanation:

An existent corner is a corner whose location can be verified by an original landmark, a surveyor's field notes, or other reliable evidence. It is the common end of two survey lines and an angle made by two boundary lines.

For example, if a land surveyor uses a tree as a landmark to mark the corner of a property, and the tree is still standing and can be identified, then that corner is an existent corner. The location of the corner can be verified by the tree, which is the original landmark.

On the other hand, a lost corner is a point in a land description, such as a landmark or natural object, whose position cannot be reasonably determined from traces of the original marks or other acceptable evidence. An obliterated corner is a corner that can be located only with evidence other than that put in place by the original surveyor.

Another meaning of corner is the acquisition of control over all or a dominant quantity of a commodity with the purpose of artificially enhancing the price, carried out by purchases and sales of the commodity. This is done in a way that depresses the market price so that the participants are enabled to purchase the commodity at satisfactory prices and withhold it from the market for a time, thereby inflating its price.

For example, if a group of investors buys up all the coffee beans in the market with the intention of driving up the price, they are creating a corner in the coffee market. This is illegal if the means are unlawful.