The phrase "firstborn son" refers to the eldest male child in a family. It indicates that this child was born before any other sons or daughters. Full definition
In order to escape the confines of the physical creation with it's laws that pertain to everything consisting of matter, as a spiritually firstborn son of the Most High, He too has to be redeemed by the Passover covenant. (redeeminggod.com)
The one who visited death on the Egyptians» firstborn sons in the dark of night, like the bad guy from an episode of «Supernatural». (religion.blogs.cnn.com)
First, they most often named firstborn sons after the father, and other sons after some other relative. (redeeminggod.com)