In Ruby what does the "receiver" refer to?

In the original Smalltalk terminology, methods on "objects" were instead refered to as messages to objects (i.e. you didn't call a method on object foo, you sent object foo a message). So foo.blah is sending the "blah" message, which the "foo" object is receiving; "foo" is the receiver of "blah".

In Ruby (and other languages that take inspiration from SmallTalk) objects are thought of as sending and receiving 'messages'.

In Ruby, Object, the base class of everything, has a send method: Object.send For example:

class Klass
  def hello
    "Hello!"
  end
end
k = Klass.new
k.send :hello     #=> "Hello!"
k.hello           #=> "Hello!"

In both of these cases k is the receiver of the 'hello' message.