Term used in the German VAT Act (§ 19 UStG). The Kleinunternehmerregelung is a simplification that grants businesses with low turnover the right to choose to be treated as non-businesses with regard to VAT. Small businesses are not required to charge and pay VAT on their invoices. In turn, however, they may not take advantage of input tax deductions from invoices of other businesses.
The regulation applies to small businesses whose total turnover plus VAT did not exceed 22,000 euros per year. A business owner is free to choose whether or not to take advantage of the Kleinunternehmerregelung.
Source: UStG, mediafon. Ratgeber Selbstständige, Wikipedia, edited (only available in German)