Off-flavors in coffee caused by poor processing, storage, or roasting. Common defects: phenolic (medicinal/plastic), moldy or musty, rioy (harsh, iodine-like), fermented (sour/vinegar), rubbery, and baggy (from poor storage in jute sacks).
Commodity coffee often has defect flavors we've normalized — that harsh, thin, bitter café coffee? Likely full of defects masked by dark roasting.