Does the Bible give us specifics about how a marriage is defined? If so, what is the definition of a biblical marriage?
Made for Relationship
The very first marriage proves that marriage is a God-ordained institution and so it has the blessing of God. Marriage was God’s idea for He said of Adam “It is not good for the man to be alone. I will make a helper suitable for him” (Gen 2:18). Mankind was made for relationships and “the man gave names to all the livestock, the birds in the sky and all the wild animals” (Gen 2:20a) but God saw that “for Adam no suitable helper was found” (Gen 2:20b). God identified the problem and then God commenced to solve that problem and so “the Lord God caused the man to fall into a deep sleep; and while he was sleeping, he took one of the man’s ribs and then closed up the place with flesh” (Gen 2:21). Then “the Lord God made a woman from the rib he had taken out of the man, and he brought her to the man” (Gen 2:22). Two important point’s surface here; first God made woman out of the same material as man was made from and the rib would seem to indicate that he and she are to stand side by side as co-equals before God as His creations. Another point is that God then “brought her to the man.” God’s intention for the woman was to stand side by side with the man. Not behind him or in front of him but beside him.
The First Marriage
Adam understood that “This is now bone of my bones and flesh of my flesh” which is why she was to “be called ‘woman,’ for she was taken out of man” (Gen 2:23). The woman was bone of his bone and flesh of his flesh and Therefore a man shall leave his father and his mother and hold fast to his wife, and they shall become one flesh” (Gen 2:24). The man was to leave his father and mother, meaning that he was to leave his family and unite with his wife as one flesh to become a new family. He was to leave and cleave. The Hebrew word for “hold fast” is really one word and it is the Hebrew word “dabaq.” It literally means “to cling, stick, cleave,” or “to join.” The two join together and stick together and become one flesh. That “one flesh” becomes a new family and at that point the two are joined together and they stick together but it is only said of the male and the female that they become “one flesh.”
The Two Become One
Notice that God tells us that “a man shall leave his father and his mother” but Adam didn’t have any physical father or mother so why did God say “a man shall leave his father and his mother?” I believe this is God’s intention; that man should leave their family and be joined to his wife. Clearly there is no room for homosexual relationships  commanded by God whereby they can be recognized as married. Why is it God-ordained for only men and women to marry? It is because she was taken out of man not out of a woman. Only the man and the woman can become one flesh. No woman and woman or no man and man can ever become “one flesh” and be joined together to stick or cleave together as far as God defines it. The structure of this sentence is that of a command, “Therefore a man shall leave his father and his mother and hold fast to his wife, and they shall become one flesh.” It is a command for the man to leave his family and I would think this means leave his family out of the man’s new family. There should never be any interference from in-laws in this new “one flesh” family. The words “a man shall” is the very same thing as “a man will” or “a man must” and is given as the only possible option. It doesn’t allow for any other possibility like “a man could” or “a man might.” There is no room for any other two to become one flesh except the man leaving his family and being joined with his wife. The male and the female “shall.become one.” Male joins with female and only a male and a female can become one flesh. Nowhere in Scripture is it said that a male and a male or a female and a female can ever become one flesh. The only possibility of the God-ordained marriage is between a male and a female.
Jesus Reaffirms Male/Female Marriage
Jesus was teaching about divorce and the Pharisees were testing Him (as usual) about allowable reasons for divorce (Matt 19:3) and Jesus reminded them of something that they should have already known that was in Genesis two; “Have you not read that he who created them from the beginning made them male and female, and said, ‘Therefore a man shall leave his father and his mother and hold fast to his wife, and the two shall become one flesh’? So they are no longer two but one flesh. What therefore God has joined together, let not man separate” (Matt 19:4-6). Here is nearly the very same thing that was mentioned in Genesis chapter two. God created them male and female and the male must leave his family and hold fast to his wife. The word for “hold fast” in the Greek is “kollaō” and means “to glue together, cement, to fasten together,” or “to fasten firmly together” so the idea is the same thing as in Genesis two. They are glued together to cleave or stick or be fastened together. The Greeks used this word for when they were gluing or cementing something together with the intent of making the bond permanent and whatever they glued together was to be considered one thing. The male and the female are now fastened or bonded permanently with one another. This “two shall (imperative, “will” or “must”) become one” is only possible when the male joins with the female. This leaves absolutely no room at all for women to be joined together to become one flesh or a male to become one flesh with another. Only a male and female must be firmly and permanently fastened to one another and only a male and female can become one flesh. There is no plan B for marriage and no other option is allowable for what God considers a one-flesh marriage.
I understand that this is not very politically correct but our standard for truth is not politics, social agendas or Supreme Court rulings . Our standard for truth is the Word of God and it never changes because God never changes. Society does change but truth is firmly fixed by the Creator of those males and females and what He says is marriage in His eyes is the only marriage that He recognizes and what He recognizes is all that is important.
Take a look at what else the Bible says about marriage: Bible Verses About Marriage 
Resource – Scripture quotations are from The Holy Bible, English Standard Version® (ESV®), copyright © 2001 by Crossway, a publishing ministry of Good News Publishers. Used by permission. All rights reserved.