Meta-A prefix term that means beyond or after (spatially). It later came to mean transcending, by the logical reasoning
The Webster says: used with the name of an discipline to designate a new but related discipline designed to deal critically with the original one (e.g. metamathematics) We also apply this prefix to objects in the meta-discipline, e.g. if the discipline deals with bars, the meta-discipline will deal with meta-bars. The system that defines the semantics for an object is made of meta-objects, part of a meta-system.
Note that etymologically, meta is just greek for "after". The use of the prefix to mean transcendence is due to the word "Metaphysics" denoting the contents of a book by Aristotle about questions of transcendence. Aristotle himself would refer to the subject of that book as First Philosophy or Theology; the title comes from Andronicus of Rhodes (1st century BC), who was the first editor of Aristotle and placed the book on the Metaphysics after the book on the Physics (Nature) in his compilation (so, it was quite literally "after" the Physics). Many centuries afterwards, people have coined the similar term Metalogic for the science that talks about Logic, and so on; since the late nineteenth century, the prefix meta- has been used systematically to coin names for sciences whose object is the study of a previous science. This is how the word shifted from its Greek meaning to the meaning it has in Latin, French and English (and presumably other modern European languages). It retains its original meaning in modern Greek. (Thanks to Derek Rayside for details).
The twentieth-century philosopher Martin Heidegger re-interpreted the Metaphysics as "things or concerns arising from the consideration of the Being of things in general", where the original word for physics, "phusis" was taken to mean any things, not just the ones we now call "physical" or "existing". Heidegger also said many useful and new things about ontology.