Gis forGrate (lid)
A grate is a piece of metal with holes in it that is used as a lid or some other covering over a larger hole. The main purpose of a grate is to let liquids through, but stop solids getting through. Grates are usually used over drains. Very large grates like the one in the picture are strong enough for cars to drive over, while still letting water drain away.
You may also be interested in grating food.
His forHatch (opening)
A manhole is a hole just large enough for an adult man to fit through. Manholes are generally used to access sewers.
A vent is an opening that lets air in or out of a building. Vents might let air flow through naturally, or have air pushed through them by a fan or air conditioner.