This is the 10792nd most frequent Russian word.
входящий
Incoming.
The word 'входящий' ( entering, incoming) is used as an adjective to describe the call ('звонок') indicating it is coming in.
Входящий звонок потребовал немедленного ответа.
The incoming call required immediate attention.
Here, 'входящую' is the feminine form of 'входящий', modifying 'корреспонденцию' (correspondence), showing correspondence that is arriving or received.
Она обработала входящую корреспонденцию за утро.
She processed the incoming correspondence during the morning.
The term 'входящий' is used figuratively to describe 'поток данных' (data stream) indicating that the stream is incoming or being received.