means ‘be afraid of/that’, it is a short form for -(으)ㄹ까 봐(서) which is ‘because (someone) is afraid of/that’. It often comes with ‘걱정이다’, ‘걱정이 되다’or ‘걱정하다’. For example,
비가 너무 많이 올까 봐 걱정이에요. I am afraid that it will rain too much.
우리 아들이 나를 닮을까 봐 걱정이에요. I am afraid that my son is going to resemble me.
발표할 때 한국어를 틀릴까 봐 걱정이에요. I am afraid that I will make mistakes in Korean on the presentation.
아이가 길을 잃어버릴 까 봐 걱정이 됐어요. I am afraid that my kid will get lost.
늦을까 봐 걱정이 돼서 일찍 출발했어요. I am afraid that I will be late, so I left early.
남자 친구가 기분 나쁠까 봐 걱정하고 있어요. I am afraid that my boyfriend will be offended.
아빠한테 혼날까 봐 말을 할 수 없어요. I am afraid that I get scolded by my dad, so I can’t tell him.