Its convenient linguistic shorthand for a common case which would be more properly be described as “a concept of a thing which does not correspond to any actual thing”. While the equivalent linguistic shorthand has been present in most languages for quite a long time, the recognition that the confusion it can sometimes produce between concepts and concrete things is a category error is, while not nearly as old, also fairly old; it is central to Kant’s argument against the ontological argument for God’s existence, for instance.