Definition:
The activity with the largest proportion of the total activity of an entity measured with the sales criterion, the number of employees or provided in the statute of an entity not conducting economic activity.

Source:

• Regulation of the Council of Ministers of 30 November 2015 on the Mode and Methodology of Running and Updating the National Official Business Register and Templates for Applications, Surveys and Certificates
  Place of publication: (Dz. U. poz. 2009, z późn. zm.)