Definition
To purposely receive a gunshot that was intended for another.
How People Actually Use It
1) To intentionally receive a bullet that was supposed to be for someone else. 2) To be able to hold any consequences for protecting someone's personality, values and interests.
"1) The criminal was about to shoot my girlfriend but I stood in front of her and took the bullet instead. 2) My anti-anime dad found an eroge game at my younger sister's bedroom and now judges her as a "worthless daughter". So I come up and take a bullet for her by explaining to my dad that if he takes away all the anime, manga, eroge and specially her friends whom she made thanks to her interests and values, she won't be the same anymore and will be someone she isn't. I also added the eroge game was mine and that I just asked her to hold it for me."
Source: Urban Dictionary