¿Difference between /yell and /shout?

Hi!
I was wondering about the difference between /yell and /shout. They have different color on chat box, but since my first language isn't english and i'm so far for a perfect english, to me, "yell" and "shout" have the same meaning. ._.

Thanks in advance. ^-^

You use /shout to let it all out.
You use rebel /yell to cry more more more.

Shout. In entire map area.
Yell. Portion of area.