The "War Guilt Clause" is the name given to Article 231 of the Treaty of Versailles. This was a controversial section, as it stated that Germany and its allies were responsible for the war, as well as for the loss and damage that Europe suffered.
Although the clause did not use the word "guilt," it did effectively blamed Germany for the war fully. This was a cause for national hummiliation in the country. Moreover, in practice, it meant that Germany had to pay for reparations, which put more strain in the already struggling economy.