MAX is a diminutive version of the latin word "maximum" meaning "the highest". In accordance with the numeral value 300, it is determined that 300 is in fact the maximum value of something the song is actually refering to.
It is well known by now that 300 (three hunderds) directly refers to the number of beats per minute, or B.P.M. for short, that the song pretends to have. Scientific test involving a computerized metronome have shown the exactitude of those claims.
To conclude, MAX 300 actually refers to the maximum B.P.M. you will encounter playing this map : 300.