The Fried Liver Attack, also called the Fegatello Attack (named after an Italian idiom meaning "dead as a piece of liver"), is a chess opening. This colourfully named opening is a variation of the Two Knights Defense in which White sacrifices a knight for a superficially impressive attack on Black's king. The opening begins with the moves:  1.e4 e5 2.Nf3 Nc6 3.Bc4 Nf6 4.Ng5 d5 5.ed5 Nxd5 6.Nxf7

This is the Two Knights Defense where White has chosen the offensive line 4.Ng5, but Black's last move is risky (other Black choices include 5...Na5, 5...Bg4, 5...b5, and 5...Nd4). White can now get an advantage with 6.d4 (the Lolli Attack). (Not according to the analysis below - NR)  However, The Fried Liver Attack involves a far more spectacular knight sacrifice on f7, defined by the moves:  6. Nxf7 Kxf7  The Fried Liver has been known for many centuries, the first known game score being from Rome in 1610.

SOURCE: https://en.wikipedia.org/wiki/Two_Knights_Defense,_Fried_Liver_Attack

The Fried Liver Attack is only a footnote in MCO-15, although GM Nick de Firmian notes (pictured above) "The old 5...Nd5 is a rare thing these days, although not clearly refuted." (MCO p 36, FN [k]