Hey muungwana! It is a widget called "system tray"
Grandpa - as you've just discovered the System Tray widget shows various apps which are running - Net Applet / Clipper / etc and KMix for sound settings.
If your KMix icon disappears again you may want to try clicking on the KMenu >> Sound > KMix and that should then drop it back in the System Tray again.
Also, by right clicking the System Tray there is an option System Tray Settings which allows you to enable/disable various items.