Comment: It's arbitrary (Score 1) 61
... so just pick one and stick to it.
I'm partial to "input" and "output" myself, from the perspective of the object using them (so a client's output goes to the server's input and vice-versa).
If you need to reference both objects' streams at the same time, you've got "myInput", "myOutput", "hisInput", and "hisOutput" for clarity.
Or just pick something fun; "spinwise" and "widdershins" isn't bad, but may confuse your users.