Fuser is a type of liquid or oil that mixes with the dry toner to turn it into a form of ink/liquid that can be sprayed onto the page and then evaporated away by the heating element in the laser printer. And codeman's suggestion/diagnosis is more than likely correct, especially with a printer that size. You can try cleaning out any dust or dirt you see with some canned air, but I wouldn't get too aggressive because you can easily break something while poking around in there. Best to wait and let a certified technician take a look at the printer.