The key

A key is a metal instrument used to open a lock .
A key used as a symbol usually signifies a secure item, location, website, digital file or connection.

And there are so many types of keys.

Key's histry is so old that 4000 years ago in Egypt.

It is also said that key was invented by Theodore of Samos.

the Middle Ages key was a symble of a city state.

And also that was symble of wives.

Flat metal keys proliferated in the early 20th century.

And now there is also electronic key.

That is used by several cars.