What does "a folk belief " mean? Is that like a superstition or an urban legend ?
I appreciated it if you gave me some concrete examples along with the explanation.

See a translation

Generally, a belief or rule held be a group of people without any scientific grounding.

A superstition is a folk belief that is known to be or believed by the speaker to be wrong.

An urban legend is a belief typically shared by a smaller group and of relatively shorter life span.

A folk belief is that if a pregnant women ties the wedding ring with a string and dangles it in front of the abdomen, depending on how the ring moves, sideways or in circle, she will have a girl or a boy.

The above is likely a superstition, but I have not seen any scientific study to confirm or reject it. It does seem out there though. So I can safely say it is a mere superstition.

Since this is a rather an old belief, I may not properly call it an urban legend. Also it did not come out in an urban environment. However some speakers may call it an urban legend. After all natural language is not mathematics.