Over-extraction
also: overextraction
Pulling too much from the grounds; tastes bitter, harsh, drying, and hollow. Fix: coarser, cooler, faster.
Over-extraction means you dissolved too much out of the grounds, dragging out the compounds that should have stayed behind. In yield terms it usually sits above the roughly 22 percent mark.
Coffee gives up its flavors in order: bright acids first, sweetness next, and harsh, bitter, drying compounds last. Push extraction too far and you collect all of that final, unpleasant fraction. The cup tastes bitter and harsh, dries the mouth (an astringent feel), loses its sweetness, and can seem hollow or ashy, with a lingering bad aftertaste. It is easy to confuse with simply over-roasted or burnt beans.
The fixes all pull extraction down. Grind coarser so water has less surface to work on, brew cooler, shorten the contact time, or reduce agitation. Change one variable at a time so you do not swing all the way into under-extraction. To diagnose which problem you actually have, taste against sour-vs-bitter, and why-is-my-coffee-bitter covers the common culprits.