The act of coming in; arrival.
"The incoming mail was piled high on his desk by noon."
In plain English: An incoming person is someone who has just arrived at your location or event.
"The incoming mail piled up on his desk by noon."
Coming (or about to come) in; arriving.
"The incoming bus arrived just as the rain started to fall."
In plain English: Incoming means something that is arriving, coming toward you, or about to happen soon.
"The incoming bus is arriving at the station in just five minutes."
a warning that something is coming towards you; especially enemy artillery fire
"The soldiers scrambled to cover as incoming shells began to rain down on their trench."
The word incoming is formed by combining the adverb in with the adjective coming to describe something that arrives or approaches. It entered English as a straightforward compound of these two existing words without any shift in its original meaning.