what is the medical term word for deficiency in blood flow?

peripheral artery disease PAD

It's hypoperfusion.

Peripheral artery disease or peripheral vascular disease (as quoted above) is merely a cause of hypoperfusion.

"Ischemia" means that a body part is not getting enough blood/oxygen.  Ischemia to a body part can be caused by a decreased blood flow (ie from low blood pressure) or total loss of blood flow from a completely blocked blood vessel.

If the tissue, such as heart muscle, dies as a result of the ischemia, it is called an "infarction."

the medical diagnosis is peripheral vascular disease (when referring to peripheral organs like the legs) or coronary artery disease (when refering to the heart). you can also use the term stenosis which means a narrowing of the arteries. for instance, carotid stenosis refers to narrowing of the carotid artery leading to inadequate perfusion to the brain.

hypoperfusion is indeed a more accurate term physiolocigally, but it's not a diagnostic term per se. also, ischemia is a result of inadequate blood flow, but the two terms are not synonymous. you can get ischemia and still have adequate blood flow in some cirumstances. for instance, with a low hemoglobin level (the main oxygen source in your blood) you may still be ischemic despite adequate blood flow, because even though you're perfusing your organs, they're still not receiving enough oxygen.,

There is a fair bit of confusion in the answers above.  Jeye's answer is technically accurate.

Ischemia is defined as local anemia due to mechanical obstruction of the blood supply.  There is no anatomic component to this; it can be peripheral, central, myocardial, cerebral, or anywhere else.

Hypoxia is the condition in which the concentration of oxygen is less than normal.  This can be due to altered blood flow (i.e., ischemia) or to decreased oxygen-carrying capacity of the blood (i.e., severe anemia).

The above are adapted directly from Stedman's Medical Dictionary, 25th edition.