In modern-day American society, a male that is over 6'2" pretty much. This is due to a lack of food and sleep caused by public schools starting too damn early in the morning and people thinking it's cool to not eat and do drugs / smoke cigarettes. A true giant is someone 6'7" or taller.
Shaquille O'Neal would be a true giant.
Idiot: How do you become a giant?
Average guy: I'm not a giant. I'm 6'3".
Idiot: How do you get so tall?
Average Guy: I eat food and get sleep.
Idiot: Woah. I wish I could do that.
Average Guy: Are you retarded?
Idiot: No u