This is a pretty broad topic. But it's an acid base imbalance caused by too
many Hydrogen ions in the blood. In can be extrinsic- like from an aspirin
ingestion or intrinsic- like from lactic acid after prolonged exercise. As a
opposed to respiratory acidosis from hypoventilation. In truth you rarely get
a pure metabolic acidosis, because the body tries to compensate by blowing off
more carbon dioxide.

Mary Murphy MD