Roland Barthes's famous essay "The Death of the Author" (1967) is a meditation on the rules of author and reader as mediated by the text. Barthes's essential argument is that the author has no sovereignty over his own words (or images, sounds, etc.) that belong to the reader who interprets them. When we encounter a literary text, says Barthes, we need not ask ourselves what the author intended in his words but what the words themselves actually say. Text employ symbols which are deciphered by readers, and since function of the text is to be read, the author and process of writing is irrelevant.
"The death of the author" notion means that meaning is not something retrieved or discovered, having been there all the while, but rather something spontaneously generated in the process of reading a text, which is an active rather than passive action. Barthes does not intend to suggest that the death of the author lets any reader read any text any way he or she like (though others aside from Barthes perused this line of thought). What Barthes is suggesting is that reading always involves at least a little bit of writing or rewriting of the text's meaning.
Barthes's "The Death of the Author" is an attack on traditional literary criticism that focused too much on trying to retrace the author's intentions and original meaning in mind. Instead Barthes asks us to adopt a more text oriented approach that focuses on the interaction of the reader, not the writer, with it. This means that the text is much more open to interpretation, much more fluid in its meaning than previously thought.
See additional summaries of works by Roland Barthes: