What exactly does it mean? I know it has to do with determining who's the best if everyone were the same size, but how does one get to be a pound for pound great? Win world titles in 2 or more weight classes? Utterly dominate your opponents in said weight classes?
'Pound for pound', 'great' and indeed now a days 'world titles' are abstract terms, with no right or wrong answers to define them, so you can put whatever value/meaning you wish to 'pound for pound'.
pound for pound actually is garbage because in the end of the day nobody cares about who is better "pfp" if an average hw can knock out a great mw. for example marvin hagler is better "pfp" but ron lyle would kill him, robinson is better "pfp" than ali, but ali would humiliate him. so pfp is trash
When a man beats a younger , taller , slimmer but heavier opponent whom was injury clear and in a good condition 2 fight and does it according 2d rules , then that man has a strong case of being considered better p4p than that opponent . doing it by a concussive stoppage makes it even clearer , but 4 a much disadvantaged man whom fights cleanly and aggressively , even lasting d distance has a lot of meaning . 4 example , a huge w8cutter like Arguello does not proven much in p4p terms 4 me , but a chubby little midget like Dingaan Thobella KOing a younger , reigning supermiddlew8 titlist and lasting d distance vs others convinces me a lot .
THE THOMPSON SUB-MACHINE GUN "The deadliest weapon, pound for pound, ever devised by man." -- Time magazine (December 1939)
I think it means the best of the best. Skills, talent and abillity combined with results when a boxer is good enough to beat his compotion.