The layman term for drain cover (grate) is manhole cover. Say "manhole cover" and floor grate cover of spies/heros using the underground sewage system popping out of manhole cover in Hollywood films appear.
Historically ever since Man invented the sewage system since the Roman Times to drain water and urban waste away for sanitation purposes, manhole covers (drain covers or grates as we prefer to call them) have already been invented out from the basic need in order to avoid people from falling into underground sewage and also to prevent large objects from entering the drains which cause choking which eventually may cause flooding.
Fast forward to the present day, the sewage system is still utilised under all cities around the world. As opposed to crude stone manhole covers the Romans use in the ancient days, now we have special steel reinforced stone gratings that provide the thousand year old function of covering the inlets of our sewage system.
More than simply a cover, check out Jonite's range of drain covers (drain gratings) here: http://www.jonite.us/products/creative-grates
