Original: After 1918, the term was used for the paramilitary organizations that sprang up around Germany as soldiers returned in defeat from World War I. They were the key Weimar paramilitary groups active during that time.
Simplified: After World War I the term was used for paramilitary units. After 1918, the word was used for the paramilitary organizations that were started in Germany by soldiers who came home after losing World War I. They were the main paramilitary groups during that time.