How long do you have to not eat for before your considered to be starving?

I don't know if there's some sort of algorithm or anything. I've been sick and all I ate for 48 hours was a single slice of toast (which I threw up) and an apple (which I kept down, yay). I'm obviously very hungry and I complained to my friend that I'm "starving". Of course we all say this but it made me wonder how long does someone have to not eat for to be considered starving