비밀?
The meaning is similar to 'secret.' If your friend tells you something and then says "비밀이에요" it means "It's a secret." So you probably shouldn't tell anyone. You might hear this 비밀 if you go the bank or maybe see it on websites. Every time I go to the bank they ask for my '비밀번호' (bi-mil-beon-ho). Literally, this means "Secret Number." Can you guess what a closer English word might be?