iOS Storyboard Presenting Segues "relationship, embed, push, modal, custom" types
A "relationship" segue is the segue between a container view controller and its child or children -- so, the initial controller of a navigation controller, the view controllers in the tabs of a tab bar controller, and the master and detail controllers of a split view controller.
An "embed" segue is the segue between a container view and the controller that's embedded in that container view that you get automatically when you add a container view to a controller's view.
Both of these segues are executed as soon as the parent controller gets instantiated. You do not call them, but you can implement prepareForSegue, and pass information to the destination view controller.