A 'Blind Box' is a term to describe a category of toys.
Where different toys from the same collection are contained in a sealed box, and nobody knows what is inside the box until you unbox the item.
Blind boxes usually come in a collection of 12 different toys, or 8, depending on the designer brands. One or two hidden/ secret toy(s) is/are usually included in a blind box toy series.
But, they are included randomly in certain sets. There is no guarantee of receiving a secret toy even if you purchase a whole set.
Pictures of all the toy designs from the same collection are usually displayed on the packaging of each blind box. What you have to do is have a lucky guess and pick the blind box that you like!