What is the difference between the terms infarction, ischaemia and penumbra?

Extent of cell death: Infarction - dead tissue. It will never come back, it is weak and can rip. Overtime it is replaced by a scar. Ischemia - tissues are starving for more blood flow, they are viable and functional. Can progress to infarction, but may stay ischemic very long time. Penumbra - zone of tissue in "twighlight" around dead zone. At risk of turning dead too, but also at risk for swelling with improved flow.