Subject to where you are from, different countries have different terms for "storm drain".

Depending on where you are from, different countries have different terms for "storm drain".
Accordingly to Wikipedia, a storm drain is essentially a tunnel that carry runoffs (rain) from urban areas. For a layman, it helps to think along the line of sewage system that operates beneath our cities.
In the US, this is commonly known as "storm drain" or "storm sewer".
In the UK, this is actually often called "surface water drain" or "surface water sewer".
In Australia and New Zealand, it is best known "stormwater drain".
And there you have it, when you hear someone mentioning "storm drain", "storm sewer", "surface water drain","surface water sewer" and "stormwater drain", you now know they mean the exact same thing.
Functions of storm drain include draining excess water (rain or storm water) and ground water from pavement, streets and carparks into rivers and streams to prevent flooding.
Although storm drains perform a amazing job of draining excess water from the urban areas, the inlets are essentially openings where left uncovered can pose a danger to pedestrians. Left uncovered, rubbish will get into 6 inch drain cover and cause choking which might eventually end up with flooding.
To ensure storm drains serve their purposes while minimizing the risks posed to pedestrians and to prevent choking of the drains, drain covers (gratings) are used to cover the inlets (openings) of the storm drains to achieve the two purposes.
At Jonite, we focus on steel reinforced drain covers (gratings) which cover your storm drains while preserving the aesthetic elements of the architecture around the drain covers.