Made popular by former WWE/F Champion, The Iron Shiek, Humbling someone would refer to defeating/humiliation someone. Shiek often uses the term in this mannner,
"I will suplex you, put you in the Camel Clutch, break your back, fuck your ass, and make you humble."
So it is debated whether it would refer to breaking someone's back, anally raping them, or a combination of the two. But most use in the way others use the word "Own" or "Pwn". The example should explain this more.
Kid 1: "Dude, your mom tasted sooooooooo good last night."
Kid 2: *punches Kid 1 in the face*
Kid 3: "Damn dude....that bitch just got Humbled."