"I am off to Prague". What does it mean? Could you explain this phrase in another words?
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"I am off to" is an idiom that means "I'm leaving for" or "I'm going to" somewhere. It can refer to an immediate departure:
or to an upcoming departure:
I suppose that it comes from "I'm taking off for [somewhere]" or "I'm going to [somewhere]" or a combination of the two, but that's just my own folk etymology.