ActionController::Base.send :include,

n one of the pluggin I saw this code Could anybody please tell what
does all this mean

ActionController::Base.send :include, helper_name
ActionController::Base.helper helper_name
ActionView::Helpers::FormBuilder.send :include, helper_name

Thanks in advance

The first line is including some instance methods into
ActionController::Base (from which ApplicationController inherits).
The second line then adds helper_name to the list of helpers available
to all controllers.
The final line does the same thing for the views.