firstborn

Definition:

The term "firstborn" refers to an offspring of people or animals that is born first, before the other offspring are born.

In the Bible, "firstborn" usually refers to the first male offspring that is born.
In Bible times, the firstborn son was given a place of prominence and twice as much of his family inheritance as the other sons.
Often it was the firstborn male of an animal that was sacrificed to God.
This concept can also be used figuratively. For example, the nation of Israel is called God's firstborn son because God gave it special privileges over other nations.
Jesus, the Son of God is called God's firstborn because of his importance and authority over everyone else.

When "firstborn" occurs in the text alone, it could also be translated as "firstborn male" or "firstborn son," since that is what is implied. (See: Assumed Knowledge and Implicit Information)
Other ways to translate this term could include "the son who was born first" or "the eldest son" or "the number one son."
When used figuratively to refer to Jesus, this could be translated with a word or phrase that means "the son who has authority over everything" or "the Son who is first in honor."
Caution: Make sure the translation of this term in reference to Jesus does not imply that he was created.