Every version of a game—parent and all clones—is bundled into a single ZIP file. This is the tidiest for your folder structure but makes it harder to delete individual versions you don't want.
A MAME ROM pack (often called a "ROM set") is a collection of game files compressed into a single archive, usually in .zip format. rom mame pack
It is important to understand that a ROM pack is not just a single game file. An arcade machine consists of multiple chips: one for the main program, one for sound, one for graphics, and often decryption keys. A MAME ROM pack contains dumps of all these separate chips grouped together. MAME uses the data from these files to reconstruct the virtual hardware of the original arcade machine. Every version of a game—parent and all clones—is