Definition
to betray someone's trust, particularly by divulging confidential information about them, or by not fulfilling a promise
背叛；告密；出賣
He ratted on his friends by reporting their plan to the police.
他背叛了朋友，向警方報告了他們的計劃。
She wanted to protect her colleague, but she was forced to rat on him to the management.
她想保護她的同事，但她被迫向管理層出賣了他。
In this circle, no one would rat someone out because no one wants to be a traitor.
在這個圈子裡，沒有人會出賣別人，因為沒有人想成為叛徒。