What does "Urtext" mean?

Until the early 20th century performers and music teachers were principally concerned with handing on to students and posterity their understanding of great works in editions including their own performance instructions and editorial changes with regard to bowing, articulation, dynamics etc.

„Instructive“ editions were presented, for example, by Artur Schnabel for the Beethoven sonatas or Clara Schumann for the piano works of Robert Schumann.

As a reaction to these editions containing major changes that had not been indicated as such, there was a movement, about the  middle of the century, to re-consider the original form of the work with a musical text free from any extraneous input.

The Bärenreiter film: insight into the editorial and production process of an Urtext edition

Bärenreiter Urtext. Introduction (pdf)