The concept of First Born or Primogeniture is the right, by law or custom, of the firstborn son to inherit the entire estate, to the exclusion of younger siblings (compare to ultimogeniture). Historically, the term implied male primogeniture, to the exclusion of females. In the absence of children, inheritance passed to collateral relatives, in order of seniority of their lines of descent. The eligible descendants of deceased elder siblings take precedence over living younger siblings, such that inheritance is settled in the manner of a depth-first search.
The principle has applied in history to inheritance of real property (land) and inherited titles and offices, most notably monarchies, continuing until modified or abolished.
With the exception of the Royal Houses in societies that were kingdoms or empires prior to them joining the Union, and about 174 other planets and numerous smaller groups on planets where that is not the general case, the concept of First Born is of very little importance.