Someone is asking why the covers for manholes are usually round (i.e. circular). They aren't always round, but often are.

"round" is "circular in shape" It's an old intelligence test question. . There are two most obvious shapes for manhole covers. Round and square. The simple reason they are usually round is that a round one cannot be easily dropped/lost down the hole, as it just does not fit though the hole.

As the person above stated - if you'd like to go more technical - a manhole cover leads to various services running under our streets, mostly sewage.

A 'manhole cover' is something you can often see on a street. If you are walking down a street and you see a round metal thing in the road, that is a 'manhole cover'. It can be pulled up, revealing a hole large enough for a person to go through. The question is asking why the covers on these holes are shaped the way they are.