Other forms: sooner; soonest
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.
The word soon is often used when there’s anticipation for something that’s about to happen. For example, “Dinner will be ready soon,” means it’ll be ready shortly. Soon can also add a sense of urgency to a request, as in “Please respond soon,” suggesting the need for a quick reply. In both cases, the word soon means that there shouldn't be a long wait.