A person who made a substantial contribution to a text, and is therefore, at least partially, responsible for its contents.

In the simplest case, the author is the person who wrote the text, but if the text is the result of a collaboration, there may be authors who did not write very much, and, conversely, the person who wrote most the text, may actually not have contributed much to the rest of the work.

In some cases, it can therefore be hard to decide who should be mentioned as author of a text, and get the credit and responsibility that comes with it.