What is the @ in RGSS scripts?

Description of the @ Syntax of the scripts in RGSS

Defines an instance variable for a class. To be able to read and write variables of this type you also need to create accessor methods for them. You can also use the attr_reader, attr_writer, or attr_accessor shortcode to load the relevant operators automatically.

Code Example:

def initialize
  @battler_name = ""
  @battler_hue = 0
  @hp = 0
  @sp = 0
  @states = []
  @states_turn = {}
  @maxhp_plus = 0
  @maxsp_plus = 0
  @str_plus = 0
  @dex_plus = 0
  @agi_plus = 0
  @int_plus = 0
  @hidden = false
  @immortal = false
  @damage_pop = false
  @damage = nil
  @critical = false
  @animation_id = 0
  @animation_hit = false
  @white_flush = false
  @blink = false
  @current_action = Game_BattleAction.new
end