stereochemistry - Does a chiral centre have to have 3 or 4 different groups attached?

I am seeing conflicting answers on the net

e.g.

A carbon atom is chiral if it has four different items bonded to it at the same position. (Wiki)

compared to

Stereocenter (chiral center): An atom with three or more different attachments (Chem.Ucla)

Why does one say 3 or more, and one say 4?

Also, there is a double bonded carbon atom here that is said to be a stereocentre, which I cannot understand. Isn't the double bond counted as two of the "same" attachments (so not even satisfying the 3 different groups criteria). How is that still a chiral centre?