What is meant by "minimal" key? I'm going though some past papers for my database exam and it asks: 


  Specify all minimal keys for R


R(A,B,C,D,E)
A → B
CD → E
E → A
B → D


I am unsure what is meant by minimal key, I've tried googling it but it only comes up with minimal superkeys. Does it just mean shortest candidate keys: CD, CA, CE, CB?

I'm getting confused as in each question he uses a different name for it and as far as I understand a minimal superkey is a candidate key?
I am in the same exam as you, I have asked Paolo what is meant by this: 
Minimal key and candidate key determine all other attributes in a relationship. 

a primary key is a candidate key chosen as the smallest number of unique attributes. 

He states that a minimal key is the fewest number of attributes so he means a primary key when he says minimal