B1
If something is secret, other people are not allowed to know about it.
Dictionary examples:
My dad's secret recipe for pancakes is just pancake mix and water. (0.0)
Our teacher's secret hobby is collecting rubber ducks. She has 500! (0.0)
The secret password to enter the treehouse? 'Broccoli is yucky!' (0.0)
This is top secret information. (21.7)
Do you think we'll manage to keep the surprise party secret from Mom until her birthday? (36.7)
The President escaped through a secret passage underneath the parliament building. (38.4)