Non Alcoholic Steatohepatitis (NASH) is a type of fatty liver disease, characterized by inflammation of the liver with concurrent fat accumulation in liver. Mere deposition of fat in the liver is termed steatosis, and together these constitute fatty liver changes.
There are two main types of fatty liver disease: alcohol-related fatty liver disease and non-alcoholic fatty liver disease (NAFLD). Risk factors for NAFLD include diabetes, obesity and metabolic syndrome. When inflammation is present it is referred to as alcoholic steatohepatitis and nonalcoholic steatohepatitis (NASH). Steatohepatitis of either cause may progress to cirrhosis, and NASH is now believed to be a frequent cause of unexplained cirrhosis (at least in Western societies). NASH is also associated with lysosomal acid lipase deficiency.
This video from THE NASH EDUCATION PROGRAM provides an excellent explanation of the current situation with NASH from some of the top experts in the field. While it's a bit long and in-depth, it's well worth your time if you need to learn more about NASH.