What is the difference between coronary artery disease and atherosclerosis?

Coronary artery disease involves impairment of blood flow through the coronary arteries, most commonly by atheromas. Clinical presentations include silent ischemia, angina pectoris, acute coronary syndromes (unstable angina, MI), and sudden cardiac death. Diagnosis is by symptoms, ECG, stress testing, and sometimes coronary angiography. Prevention consists of modifying reversible risk factors (eg, hypercholesterolemia, hypertension, physical inactivity, obesity, and smoking). Treatment includes drugs and procedures to reduce ischemia and restore or improve coronary blood flow.
Atherosclerosis is patchy intimal plaques (atheromas) in medium-sized and large arteries; the plaques contain lipids, inflammatory cells, smooth muscle cells, and connective tissue. Risk factors include dyslipidemia, diabetes, cigarette smoking, family history, sedentary lifestyle, obesity, and hypertension. Symptoms develop when growth or rupture of the plaque reduces or obstructs blood flow; symptoms vary by artery affected. Diagnosis is clinical and confirmed by angiography, ultrasonography, or other imaging tests. Treatment includes risk factor and dietary modification, physical activity, antiplatelet drugs, and antiatherogenic drugs.

atherosclerosis is thickening and hardening of the arteries in general. Coronary artery disease is thickening and hardening of the coronary arteries. CAD is essentially atherosclerosis of the coronary arteries.

Atherosclerosis can occur anywhere in the body. CAD is atherosclerosis occuring in the coronary arteries (and later possibly leading to angina, myocardial infarction (heart attack), etc)

they're basically the same, atherosclerosis being the scientific term