亲(qīn) - close, dear, related by blood; to kiss in Mandarin

亲 (qīn) is the character of closeness by blood and by affection. As an adjective it means close in a relationship: 他们很亲, 我跟她不太亲. In front of a kinship term it means full or biological rather than step or in-law: 亲哥哥 is your brother by the same parents, 亲生父母 are your birth parents, and 亲人 covers your immediate family.

It is also a verb meaning to kiss, usually reduplicated for a light affectionate peck: 亲了亲, 亲一下. That register matters. 亲 is what parents do to children and couples do casually; 吻 (wěn) is the weightier, more literary word.

Two things trip English speakers. First, 亲 is rarely a free word in written Mandarin outside these uses, so most of the time you will meet it in compounds: 亲爱 (dear), 亲自 (in person), 亲切 (warm, kindly), 父亲 and 母亲 (father, mother). Second, on Chinese shopping apps 亲 has become a breezy way for sellers to address a customer, roughly hi there. Do not carry that use into ordinary conversation.