I think this refers to some kind of floor covering, often aluminium or steel, that has a raised 'tread' pattern — typically, little sort of diamond-shaped bumps — so as to make it less slippy.
This is one kind, although there are many other designs:
http://www.aluminiumdiscs.com/sale-5356667-for-non-slip-alum...Please note that here, 'tread' refers to the raised pattern (like on a tyre) and does NOT refer to the treads on stairs (although of course this type of material is indeed commonly used on stairs too!)