1. A revision is the introduction of intentional changes into a text in its transmission, either by an anonymous scribe or a less anonymous redactor. The term is usually reserved for more substantial changes, and typically changes for a specific purpose, such as updating the text or adding new material. Revisions tend to increase the length of the text (lectio brevior), but there are also examples of revisions which consist of text reduction or simplification, e.g. in epitomes. The word 'revision' may mean the process or the result; the result can be called a recension, redaction, or version. (For a further discussion, cf. recension).
2. More narrowly one often means by revision (or more fully 'authorial revision') a revision made to a text by its author himself. This process can have important consequences for the stemma, as it may lead to more than one original text state from which witnesses are copied.