Peepbo is the little game grown-ups play with babies: you hide your face, then show it again, and the baby laughs. British English often writes peepbo or peep-bo; American English almost always says peekaboo. You cover your eyes, duck behind a cloth, or hold up a book, and then pop out. It lives in nurseries, picture books, and grandparent-talk — not in the office, and not in a serious essay. Though actually, the game is one thing and the shout is another: people also cry “peep-bo!” at the moment of showing their face, the same kind of noise as “boo”. Older British speakers are the ones who still use the word; younger ones often just say peekaboo even in Britain.