High ALT levels

So I gather that the healthy 'ALT' level in one's blood is between 8-31 U/L.  Well, what IS the ALT level anyway?  what does ALT stand for?  What causes your ALT to rise and fall?  And what would be happening, what would be the probable cause, and what would the symptoms be if one's level were:
08 Oct: 13
31 Oct: 201 H
01 Nov: 179 H
02 Nov: 213 H
?

[SassyLassie]

Typically used to detect damage to the liver, they often do this test along with the other liver function tests that you mentioned. Have you been having difficulties with your liver?

I noticed these numbers are high as well.