Apoplexy is bleeding into an organ or loss of blood flow to an organ. For example, adrenal apoplexy is bleeding into the adrenal glands, pituitary apoplexy is bleeding into the pituitary gland, and so on.

When the word apoplexy (with no organ specified) is used alone, it often refers to stroke symptoms that occur suddenly. Such symptoms can be caused by bleeding into the brain or by a blood clot in a brain blood vessel. Conditions such as subarachnoid hemorrhage or stroke are sometimes called apoplexy.

Functional apoplexy is when a person appears to be having stroke-like symptoms but there is no brain abnormality.