Meaning of “Oshi(推し)”

“Oshi(推し)” means a person who I support.
If you are someone’s big fan, it means your oshi(推し) is the someone.
And if someone ask you “Dare oshi(誰推し)?”, it means “Who is your oshi(推し)” or “Who’s your favorite?”.
Then you should answer “[Someone’s name you love and support] oshi(推し)”.

I’ll give you additional information which is related with “oshi(推し)”.

“Hako oshi(箱推し)” means you’re a fan of whole members of the group.
“Hako(箱)” means box.

“Oshi mem(推しメン)” means a member you support.
In this case, mem(メン) is an abbreviation for member(メンバー).

“Oshi hen(推し変)” means changing own oshi.
“Hen(変)” is an abbreviation for “Henkou(変更)” which means change.

By the way, “Oshi(推し)” as a noun sounds like a slang, maybe Otaku’s slang just a bit, but as a verb like “Oshi te iru(推している)” or “Osu(推す)” is not a slang.

Example Conversation

A: Actually, I’m morota(モーヲタ) too.
(Morota(モーヲタ) is an abbreviation for モーニング娘ヲタク(Morning musume otaku), “Morning musume” is a Japanese Idol group.)
B: Seriously? You should have told me earlier! Dare oshi(誰推し)?
A: Marchan oshi!! Dare oshi(誰推し)?
B: I used to have a oshi mem(推しメン), but now I’m hako oshi(箱推し).

A: 実は私もモーヲタなんだよね。
B: まじで！？早く言ってよ！！え、誰推し？
A: まーちゃん推し！誰推し？
B: 前は推しメンいたけど、今は箱推しなんだよね。