When people refer to metal balls as ball bearings. A ball bearing is an assembly of outer ring, inner ring, balls, and a cage/retainer. I worked in bearing manufacture for years and they’re just referred to as balls. To be more specific, it would be a bearing ball, not a ball bearing.
When I was a kid, I heard that leaving cut grass on the ground was better for your lawn. Surprisingly, this was enough to convince my dad that I didn’t need to bag the clippings when mowing.