What does `.call` do in Ruby, and how is it used?

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1

What does .call do in Ruby, and how is it used?

I came across this method where .call is used at the end:

def allow?(controller, action, resource = nil)
  allowed = @allow_all || @allowed_actions[[controller.to_s, action.to_s]]
  allowed && (allowed == true || resource && allowed.call(resource))
end

However, the documentation doesn’t clearly explain when or how to use .call. Can someone clarify its purpose and provide examples of call Ruby usage?