Meaning of “Urayama(裏山)”

Urayama(裏山) means “I envy you” as an internet slang.
Urayama(裏山) is an abbreviation for “Urayamasii(羨ましい：うらやましい)”;

Basically urayama(裏山) means “the hill back of one’s home” and if you want to shorten “Urayamasii(羨ましい)”, it must be “Urayama(羨ま)” not “Urayama(裏山)”.
But it’s easier for us and computers to use “Urayama(裏山)” when we convert “うらやま(Urayama)” into Kanji.
If you type “Urayamasii”, the computer can use the kanji:羨 which is correct one, but we want to skip to type “sii” so then, Using “裏山” is the only way.

Why do we want to skip “sii”?
Because Japanese like to shorten words to three or four characters.
You should remember this!!

Example Conversation

A: Guess what? I won the raffle of PlayStation5!!
B: Seriously? Oh, really Urayama! The odds of it were 1 in 40, wow, you’re lucky.

A: 聞いて！！PS5購入権の抽選あたった！！！
B: え、まじ裏山。倍率40倍だろ？すげーな。

(By the way, A is me, yes, I won the raffle of PlayStation5!! Yeahhhh!!)