A request or favor; something one asks for. The polite prefix お- is often used.
七夕にお願い事を短冊に書いた。
I wrote my wish on a strip of paper for Tanabata.
友達に小さなお願い事を頼んだ。
I asked a friend for a small favor.
お願い事があるときは、はっきり伝えたほうがいい。
When you have a request, it's better to state it clearly.