the act of meddling in someone’s affairs (and trying to help them out without being asked)
ありがた迷惑, 大きなお世話, 首を突っ込む
It is a synonym of ありがた迷惑; the minor difference is that while ありがた迷惑 describes someone’s favour with a bit of irony, お節介 often describes your annoyance like “That’s is none of your business”.
It is often used as お節介を焼(や)く, and people who do お節介 are described as お節介な人.
I’ve never asked this but one of my friends is trying to help me get together with him. Honestly, it’s an unpleasant favour.