this is a tough question...mostly because it can largely be based on comparison. i used to think entirely in numbers, but gave no real thought to relative strength (benching over 200 meant you were strong, regardless of your weight). now my definition has really broadened and i look to fitness standard tests to tell me what i need to know. this is the post mark did on fitness tests:
Physical Fitness Standards | Mark's Daily Apple
granted, these are all-around fitness, but i think you have to be pretty strong to complete them. i'm sure there are plenty of hugely muscled, strong as an ox people who couldn't do well in these because of the calisthenic and cardio nature of them...but, my thing is, what's the point in being that strong if you can't effectively move your own body?