What does the medical abbreviation ALT mean?

ALT stands for alamine aminotransferase. Sometimes it's also called SGPT. It's part of the liver function tests.
alanine aminotransferase
This stands for alanine transaminase and is a liver enzyme that is released when liver cells "burst" on being damaged.
it means alanine transaminase . It is a enzyme from liver cells. When there is an injury to the liver, the cells die and its contents (including AST) are launched in the blood. So, if ast is high, there propably was a liver injury.