Coffee beans that have had ~97-99% of their caffeine removed before roasting. The bean still tastes like coffee — most of the flavour compounds aren't caffeine — but it won't keep you up at night. Specialty decaf has gotten dramatically better in the last decade as the decaffeination processes have improved.
How caffeine is removed
Caffeine is water-soluble. Every commercial decaffeination method exploits that, but they differ in what else they take with the caffeine and what they leave behind in the bean. Three approaches dominate:
Swiss Water Process (SWP). Green beans are soaked in water, the water becomes saturated with both caffeine and flavour compounds, then the water is run through a charcoal filter that captures caffeine specifically. The cleaned water (now caffeine-free but still flavour-saturated) is reused to soak fresh batches — caffeine leaves but flavour stays. Chemical-free, expensive, popular in specialty.
Sugar Cane Process / Ethyl Acetate (EA). Beans are soaked, then washed in ethyl acetate — a solvent that bonds with caffeine but not with most flavour compounds. EA is a naturally occurring compound (found in fruit, including the molasses byproduct of sugar cane fermentation, hence the name). Faster and cheaper than SWP. Mostly Colombian.
CO₂ / Supercritical CO₂. Pressurized carbon dioxide acts as a selective solvent that pulls caffeine out without disturbing flavour. Industrial-scale, used by Illy and large roasters. Cleanest cup of any decaf process when done well.
Methylene Chloride (DCM / European process). A solvent process that's banned in some markets but legal in many. Produces good cup quality but specialty-tier roasters mostly avoid it now for marketing reasons.
What to expect from specialty decaf
Done well, modern decafs cup at 84-87 points — solidly in specialty territory. The biggest tells: lower body, slightly muted aromatics, a tiny "decaf signature" that experienced cuppers learn to identify but most drinkers won't notice. Brewing is otherwise identical.
A great decaf is harder to find than a great regular coffee — most farms don't bother with the extra cost — but they exist, especially from roasters who explicitly source for decaf quality.