It's not necessarily a comedy show like you can see on TV ("Knallerfrauen" or whatever). It's an event on a stage, with a usually not very big audience, where one or at most a few persons talk, maybe sing or play an instrument, mime or entertain the audience in another way. In political cabaret, current events, current actions of politicians etc. are commented on directly or indirectly often in a witty, satirical and ironic way. It's critical in the sense they want to expose stupid actions or viewpoints, often by exaggeration. If you can watch youtube where you are, and if your spoken comprehension is good enough, search for "Volker Pispers" or "Dieter Hildebrandt" for some examples of political cabaret.

Kabarettisten are cabaret artists. http://en.wikipedia.org/wiki/Cabaret Yes, ge­sell­schafts­kri­tisch means critical of the society. You can use an on-line dictionary to check the meanings of German words, e.g. www.dict.cc/ (Grman/English)