The meaning of SOON is without undue time lapse : before long. How to use soon in a sentence. Usage of Safe: Usage Guide
If something is going to happen soon, it will happen after a short time. If something happened soon after a particular time or event, it happened a short time after it. You'll be hearing from us very soon. This chance has come sooner than I expected.
soon (so̅o̅n), adv., -er, -est. within a short period after this or that time, event, etc.: We shall know soon after he calls. before long; in the near future; at an early date: Let's leave soon. promptly or quickly: He came as soon as he could. readily or willingly: I would as soon walk as ride. early in a period of time; before the time specified is much advanced: soon at night; soon in ...
When someone says they'll be arriving soon, it means you won't have to wait much longer for them to show up because they will be there in the near future.