A mop is either a specially made or home made marker that is designed to have a large nib and to provide more ink or paint to the surface than a common pump action or capillary marker. Mops can contain either ink for indoor use or paint for outdoor use and usually contain a thin paint or ink and are squeezable to control the flow of paint or ink to the nib as to produce drips.
Home made mops were invented in New York City as a means to have a wider more durable marker by stuffing felt chalk eraser into a variety of containers and filling it with whatever ink was on hand, usually flow master, grocery ink (garvey), home made carbon paper ink, and an assortment of other inks. Currently home made mops can use "oldschool" methods of eraser and a container of ink or can be paint or ink filled into a variety of applicators including those for shoe dye or "allwhite". A common mix for a shoe dye sponge tip mop is silver oil based paint thinned down with oil based thinner as to flow better and drip.
Commercially made mops can either be empty or filled with inks or paints. A popular brand on the market is Krink which sells a large shoe dye style mop, paint mops in various colors, four colors of ink mops and a line of steel tipped mops. Some commercially made mops include a cap at the end to make filling easy and can have nibs up to an inch wide or more. The only downside to commercially made mops is that they lack the possibility to get calligraphic lines like that of markers or home made mops.