Jealousy

What is jealousy?
For a long time I've been thinking for the meaning.
I've never been jealous or at least not for a guy or girl actually it was only for food, so seriously I've never been jealous..

But I don't know One of these last days I've felt jealous and it was wooo haha xD
I know I seem strange but really I've never been jealous, my parents too said it :)