A character is desirous of an advantage perceived to be held by another, whether it be material (fancy hat) or intangible (love, friends, power, ability, fame, etc.).

Examples:
Janice Lester went insane with jealousy over the achievements of her one time lover Captain Kirk in tos3x24 "Turnabout Intruder".

References:
https://en.wikipedia.org/wiki/Jealousy