I know what a fatty liver mean but what do they mean when they say they say it's borderline mild?

Nothing: Fatty infiltration of the liver is quite common and only rarely problematic. You simply need to have routine blood testing yearly.

Fatty Liver : Steatohepatitis , or "fatty liver" can be due to a number of causes. If biopsied, pathologists can "grade" the process if it is accompanied by inflammations and drop out of cells, as "mild, " "moderate, " or "severe." liver function test values alone do not correlate well with the biopsy picture, so if you haven't had a biopsy your doctor may be reacting to your ast and alt values.

Slightly abnormal: Fatty liver is a sonographic/radiologic finding and is graded mild, moderate, or severe etc.. Each liver has some fatty infitration, but above certain level then it is termed fatty liver--the most common liver disease in us today (obesity epidemic). Borderline means just at higher end of normal-lower end of abnormal (mild fatty liver). Weight likely will help reverse this. Consult doc. Good luck.