the.com/pearl onion

means A tiny, mild onion harvested young, usually no bigger than a marble, prized for pickling or skewering rather than slicing into rings.

from The name is purely descriptive, not botanical — these aren't a special dwarf species of onion, just ordinary onions pulled early or grown in crowded conditions so they stay small and round. 'Pearl' entered the name for the obvious reason: the small, pale, lustrous bulbs look like little pearls, the same logic behind 'pearl barley' or 'pearl sugar,' where 'pearl' just means small, round, and gleaming.