Apex classes cannot be static.
Static allowed only in outer class.
Static variables not transferred as a part of View State.
Static variables and static block runs in order in which they are written in class.
Static variables are static only in scope of request.
static: This keyword defines a method/variable that is only initialized once, and is associated with an (outer) class, and initialization code. We can call static variables/methods by class name directly. No need of creating instance of a class.