What is the difference between chiral and stereocenter?
Chiral refers to a specific type of stereocentre.
A stereocentre is a point within a molecule (it could be an atom but it doesn't have to be, it could just be any geometric point) that is surrounded by groups of atoms such that if one was to swap any two of the groups you would obtain a stereoisomer.
Chirality, on the other hand, refers specifically to atoms, and to an atom with other atoms or groups bonded to it in such a way that the resulting species cannot be superimposed on its own mirror image.
The terms are often used interchangeably, but this is actually incorrect (or at least inaccurate). A chiral centre is a specific type of stereocentre.