I'm not sure I follow you on this. Can you rephrase it?
It stands for Interprocess communication. Some methods to take note of are DDE (outdated), file-based communication, [api]SendMessage[/api] with/without WM_COPYDATA, [api]ReadProcessMemory[/api]/[api]WriteProcessMemory[/api], and System.Runtime.Remoting. This last one is solely related to .NET.