Philosophy of Language is the reasoned inquiry into the origins of language, the nature of meaning, the usage and cognition of language, and the relationship between language and reality. It overlaps to some extent with the study of Epistemology, Logic, Philosophy of Mind and other fields (including linguistics and psychology), although for many Analytic Philosophers it is an important discipline in its own right.
It asks questions like "What is meaning?", "How does language refer to the real world?", "Is language learned or is it innate?", "How does the meaning of a sentence emerge out of its parts?"