Some nouns have a different meaning in plural.

Единственное число (Singular)

The needle of a compass always points north.
It is an English custom to celebrate the Queen's birthday.

She has a lot of experience working with children.

Множественное число (Plural)

You can draw perfect circles with compasses.
When he got off the plane, his bag was searched at customs.

The main characters in the book had been through a lot of bad experiences.
He can't see very well without his glasses.