In textual criticism an innovation is a change introduced at some point into a textual tradition. It is basically a positive expression for the Lachmannian notion of error, cf. also secondary reading. As it is more positive it will be used more for conscious and goal-driven interventions by scribes into texts (which can only be called errors by stretching the normal use of this word quite far). Stemmata are rooted by considering common errors (that is: shared innovation) only. Witnesses that share only readings that are not innovations, are not closely related as the archetype will already have contained these readings.
The notion of shared innovation is also used in linguistics. In historical linguistics the contrary to innovation is 'archaism'.
In other languages