In any online chat
software, the "inputline" is whichever little box into which you type the text you want to be sent.
In most IRC programs for *n?x and Windows, this is a little one-or-two-line pane tacked to the bottom of each chat window. Macintosh IRC clients tend to take the tack of using a floating windoid which contains one single inputline shared by all windows-- anything typed is sent to whatever window is active. (ShadowIRC is still capable of maintaining seperate chat history buffers for each channel, though.) The sole reason for this difference is that Microsoft Windows and X both just happen to really suck at handling windoids.