The name Papiermark (English: paper mark, officially just Mark, sign: ℳ) is applied to the German currency from the 4th August 1914 when the link between the Goldmark and gold was abandoned, due to the outbreak of World War I.
In particular, the name is used for the banknotes issued during the hyperinflation in Germany of 1922 and especially 1923 (see Inflation in the Weimar Republic), which was a result of the German government's decision to pay its war debt by printing banknotes.
From 1914, the value of the Mark fell. The rate of inflation rose following the end of World War I and reached its highest point in October 1923. The currency was stabilized in November, 1923 after the announcement of the creation of the Rentenmark, although the Rentenmark did not come into circulation until 1924. When it did, it replaced the Papiermark at the rate of 1 trillion Papiermark = 1 Rentenmark. Later in 1924, the Rentenmark was replaced by the Reichsmark.
Here is a 1000 Mark banknote, over-stamped in red with "Eine Milliarde Mark" long scale (1,000,000,000 mark), issued in Germany during the hyperinflation of 1923.
Obverse: German mint master Jorg Herz
Reverse: Value
The victor nations in World War I decided to assess Germany for their costs of conducting the war against Germany. With no means of paying in gold or currency backed by reserves, Germany ran the presses, causing the value of the Mark to collapse. Many Germans literally carted wheelbarrows of cash to pay for groceries.
During the hyperinflation, ever higher denominations of banknotes were issued by the Reichsbank and other institutions (notably the Reichsbahn railway company). The Papiermark was produced and circulated in enormously large quantities. Before the war, the highest denomination was 1000 Mark, equivalent to approximately 50 British pounds or 238 US dollars. In early 1922, 10,000-Mark notes were introduced, followed by 100,000 and 1 million Mark notes in February 1923. July 1923 saw notes up to 50 million Mark, with 10 milliard (1010) Mark notes introduced in September. The hyperinflation peaked in October 1923 and banknote denominations rose to 100 billion (1014) Mark. At the end of the hyperinflation, these notes were worth approximately 5 pounds or 24 dollars.
Note on numeration: In German, Milliarde is 1,000,000,000, or one thousand million, while Billion is 1,000,000,000,000, or one million million.