病灶 is a medical term for the precise spot in the body where disease is centered - a lesion, infection focus, or tumor site. Often used metaphorically in journalism: 腐败的病灶 ('the focal point of corruption').
memory
病 'illness' + 灶 'cooking stove / hearth' → 'the hearth of the disease', i.e. where it burns hottest. The metaphor of disease as fire smoldering at a focal point is striking - once you see it, the word sticks.
