What does "alienation" mean in Brecht's plays?

Brecht sometimes uses Marx's philosophical term "alienation" and sometimes "defamiliarization". It requires the playwright to observe life with his unique insight, and to explore and show the unusual connotation contained in ordinary life, so that people can have a shock of "strangeness", so as to think about it and explore the origin of things. Only in this way can drama have the function of understanding and transforming the world.