OAP is a British short way of saying old-age pensioner: a person old enough to get a pension from the state. You see it on signs and in everyday UK talk about cheaper tickets, free bus travel, and special times at the swimming pool. It is not rude in the old newspaper sense — people say it the way they say student or child, as a group label — though actually some older people would rather be called a pensioner or a senior, because OAP can feel like a tag stuck on you. It is not a job title and not a medical word. Outside Britain and Ireland you will hear it much less; American English prefers senior or retiree, and it is not a short form Taiwanese English uses. Say the three letters, not a word that sounds like “ohp.”

領國家年金的長者（英式說法；台灣會說領退休金或國民年金的人，較少用這個縮寫）