2 categories of acute myocardial infarction a STEMI and an NSTEMI
in both case the MI stands for myocardial infarction and the front end of the terms is telling you what type of MI it is depending on information obtained from the ECG
So, we have myocardial infarctions in which the ST segment of the ECG is elevated (STEMI) and a myocardial infarction in where the ST segment is not elevated (NSTEMI)
In terms of severity the STEMI is a far more severe form of MI than the NSTEMI