A key is a small tool usually made of metal. People use it to open or lock doors, boxes, or cars.
I have lost my house key.
She put the key in the door.
This meaning uses 'key' in a figurative way. It means an important thing that helps solve a problem or understand something.
Hard work is the key to success.
Trust is the key in a good friendship.
A key here means a guide or system used to understand signs or symbols. For example, in maps or music, it helps people read correctly.
The music key is C major.
The map has a key for the symbols.
This meaning means a button on a keyboard or instrument. When you press it, it makes a letter, number, or sound.
Press the space key to start.
The piano keys are black and white.
Here, 'key' means one of the buttons you press on a piano or computer keyboard to make a sound or write a letter.
He played fast on the piano keys.
She typed quickly on the computer key.
This verb means to press keys or buttons on a keyboard or machine to put in data or control it.
Please key in your password.
He keyed the numbers quickly.
