If you are asking about actual class and class instance variables here's a brief explanation. If you're talking about variables that show up in view templates or somewhere else then please be more descriptive with your question.
Class variables in ruby persist throughout a whole class hierarchy.
class A @@a = 1
def self.a ; @@a ; end end
A.a # => 1
class B < A @@a = 2 end
A.a # => 2 B.a # => 2
Class instance variables on the other hand exist in the context of a single class definition.
class C @c = 1 def self.c ; @c ; end end
C.c # => 1
class D < C @c = 2 end
C.c # => 1 D.c # => 2