This indicates a bulk compilation. Rather than downloading individual galleries, these ZIP files are bundled to preserve a chronological range of a studio's output. The Rise of Eastern European Digital Studios
Refers to the geographic origin of the production or the subjects. Gentle Angels: The specific series or "sub-brand" name. LS-Ukrainian--Gentle--Angels-Sets-151-175.zip
Open-source and handles almost any compression format. This indicates a bulk compilation