It's a term of endearment, like sweetheart, or honey, you know?

[This isn't actually the first time he's had to explain this, so he's not too worried.

In answer to Cassian's question, Taako just makes a little poof gesture with his hands, which is what will happen to any ghosts.]

Lovely to meet you, Jyn. [He sounds very amused, also not bothered about the fact she didn't give her name.] Nice to run into someone else with a food-slash-beverage for a name.