Difference between Class variables and Reference variables

'abc' could be a private instance variable (if it's declared at class level) or a local variable (if it's defined within a method or property).

If Student is a class, then it's a reference type or object variable.

If Student is a struct, then it's a value type or value variable.

The term 'object' is not normally used with value types in .NET.

However, the term 'instance' can be applied to either classes or structs so 'abc' could be termed an instance variable in either case.
 

Thanks....

Student abc = new Student(); is a object variable or reference variables ?

Class (or static) variables apply to the class as a whole and not to a particular instance of it. Consequently, there is only one copy of a class variable which persists for the lifetime of the application.

In contrast, instance variables apply to a particular instance and so each instance has its own copy which persists until the instance is garbage collected.

From outside the class and provided they are accessible, class variables are always accessed by prefixing them with the class name whereas instance variables are accessed through a reference to the instance in question.