One Shot: A Definition
So often people say "OMG HE ONE SHOT ME" or "ITS ZED, DON'T TAKE insert champ here HE CAN ONE SHOT YOU".
I'd like to enlighten you. "One shot" is a term that means the enemy took your HP from 100% to 0% (Or in recent times anything from about 75%+ to 0%) while only using one spell, attack, or ability, that does damage. As such, champions such as the aforementioned, Zed, can not "one shot" anyone. There are in fact, very few champions who can. Nasus and Veigar are those that immediately come to mind. When a champion such as Zed, Lux, LB, or Annie, can kill you in little over one second that is not called "one shot". That is what is known as a burst.
Thank-you, and you're welcome.
EDIT: Many people are still defending themselves in that a "one shot" can be a "one combo kill". The answer is no. a "one shot" means One Shot. A one combo kill is a burst.

>.> ) kills you from full, or at least near full. If you're at half health, the one skill killing you isn't 'one-shot' either
dat ult scaling tho
