When cleaning print heads what's the white bit underneath

[Tricia]

Sorry for silly question but what's the white bit that runs underneath the print heads. If you get it all dirty when trying to clean the print heads is the printer ruined? I've tried googling but have no idea what that white line of stuff underneath is and how important it is to keep clean. lol I did put something underneath to soak the solution up but sadly I must have put too much in.