Is it offensive to call someone dear?
It certainly doesn’t sound disrespectful. It’s just a friendly greeting. Using a term of endearment in person is really quite different to addressing someone on an internet forum as “my dear” or even just “dear”.
What does dear mean from a girl?
It means the same as “honey,” or “sweetheart.” Older people who’ve been married a long time might call each other “dear.” Or a grandmother might call her granddaughter “dear.” I don’t know a lot of young people who call each other dear. It’s kind of an old fashioned word.