emotion
that "occurs when a person lacks another's (perceived) superior quality, achievement, or possession and either desires it or wishes that the other lacked it."
Envy can also derive from a sense of low self-esteem
that results from an upward social comparison threatening a person's self image
: another person has something that the envier considers to be important
to have.
O! beware, my lord, of jealousy; It is the green-ey'd monster which doth mock The meat it feeds on. 
ENVY, n. Emulation adapted to the meanest capacity.
Envy and wrath shorten the life.
This only grant me, that my means may lie Too low for envy, for contempt too high.
It is the practice of the multitude to bark at eminent men, as little dogs do at strangers.
If we did but know how little some enjoy of the great things that they possess, there would not be much envy in the world.