¿Qué significa "address" in this sentence ?

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"Address" in this sentence is talking about how you might refer to someone. Like how in Japan you might "address" someone you just met by adding "San" to their name out of respect. Or how in the US you might address a teacher as "Mr., Ms., or Mrs.". How you might "address" someone is not always a formal thing though, again it's just how you may refer to someone. In the US close friends sometimes address each other with insults (ya it's weird haha), e.g. When they meet up somewhere to hang out, they might address each other as "butt-face" when first meeting, e.g. "what's up butt-face?".

I hope this helps at least a little! Let me know if you have more questions or need more clarification.