Photobomb means to drop in a photo unexpectedly or to hop in a picture right before it is taken.
照片炸弹指意外被拍进照片里或者在照片拍摄的一瞬间进入镜头范围的行为。
It can also refer to an otherwise normal photo that has been ruined or spoiled by someone who was not supposed to be in the photograph.
另外,照片炸弹也可以指本来正常拍摄的一张照片因为不相干人的出现而使照片失去原有的意义。
The most common photobomb is someone in the background making a face.
最常见的照片炸弹就是有人在照片背景里做鬼脸。