Blade grinder
also: propeller grinder, spice grinder
A cheap grinder that chops beans with a spinning blade, producing very uneven dust and chunks; best avoided for coffee.
A blade grinder uses a fast-spinning propeller blade, the same idea as a small spice or herb grinder, to chop beans by smashing whatever it hits. It does not set a particle size; you control grind only by how long you run it.
Why it matters: chopping is random, so a blade grinder produces a chaotic mix of fine dust and large chunks at the same time, lots of fines alongside boulders. When you brew, the dust over-extracts into bitterness while the chunks under-extract into sourness, so the same cup tastes both sour and bitter. The blade also generates heat that can dull aroma.
It is cheap and widely sold, which is why beginners often start here, but it caps how good your coffee can get no matter the beans or method. The reliable upgrade is a burr grinder, which sets a uniform, adjustable size. See burr-vs-blade and blade-vs-burr-grinder for a fuller comparison.