In plain words
Input is what enters the system so the computer has something to respond to or process.
Why learners confuse it
Many devices do both input and output jobs, so it helps to name which direction the information is moving.
Input is information that goes into the computer.
When people cannot tell input from output, device problems become much harder to name clearly.
Input is what the computer receives from a person, device, or another system.
Input is what you give to the computer so it has something to work with.
Input is what enters the system so the computer has something to respond to or process.
Many devices do both input and output jobs, so it helps to name which direction the information is moving.
Study the larger concept after the word itself becomes clear.