The scope of a variable refers to where in the program it can be accessed. There are three levels of variable scope in Ruby:

1. Local scope: Variables declared within a method are only accessible within that method.

    def my_method
      x = 10
      puts x
    end

    my_method # prints 10
    puts x # undefined local variable or method `x' for main:Object

2. Instance scope: Instance variables (denoted by the @ symbol) are accessible within the current instance of a class and any methods defined within that instance.

    class MyClass
      def initialize
        @x = 10
      end

      def my_method
        puts @x
      end
    end

    obj = MyClass.new
    obj.my_method # prints 10
    puts obj.x # undefined method `x' for # (NoMethodError)

3. Global scope: Variables declared outside of any method or class are accessible throughout the program.

    $x = 10

    def my_method
      puts $x
    end

    my_method # prints 10
    puts $x # prints 10

        It's generally recommended to use local scope as much as possible to avoid naming conflicts and to make code easier to reason about. Instance scope is useful when you want to share data between methods within a single object, and global scope should be used sparingly as it can introduce unexpected behavior and make code harder to maintain.