hill behind a house or village
Refers to the mountain or hill directly behind a settlement, often part of the local landscape.
There is a small shrine on the hill behind my house.
shady side of a mountain
The side of a mountain that receives little direct sunlight; often cooler and damper.
The shady side of the mountain gets no sun, so moss grows thickly there.
Internet slang pun on うらやましい (envious); used humorously to express jealousy.
See also: 羨ましい
I'm so jelly of that person's new car!
Compound of 裏 (ura, 'back') and 山 (yama, 'mountain'). The slang sense is a wordplay on うらやましい (urayamashii, 'envious').