Merriam-Webster online says:
(1): the state of being united to a person of the opposite sex as husband or wife in a consensual and contractual relationship recognized by law
(2) : the state of being united to a person of the same sex in a relationship like that of a traditional marriage
(marriage: b: the mutual relation of married persons"

Strongs says:
(In the Old Testament, `ownah {o-naw'}.
1) cohabitation, conjugal rights

(In the New Testament, gamos {gam'-os}
1) a wedding or marriage festival, a wedding banquet, a wedding feast
2) marriage, matrimony

What are the Biblical requirements for considering oneself to be "married"? (What does the Bible say?)

1) Marriage is God's invention
Genesis 2:18 "Then the LORD God said, "It is not good that the man should be alone; I will make him a helper fit for him."

2) Marriage means to leave and hold fast
Genesis 2:24 "Therefore a man shall leave his father and his mother and hold fast to his wife, and they shall become one flesh."

3) Marriage is a covenant - and God is the witness.
Malachi 2:14 "But you say, "Why does he not?" Because the LORD was witness between you and the wife of your youth, to whom you have been faithless, though she is your companion and your wife by covenant."

4) Marriage is a relationship that is recognized and/or regulated by law.
Romans 13:1 "Let every person be subject to the governing authorities." Unless we have a real reason to believe that the state is asking us to sin by following the law in order to be married, we must obey the laws of the land.

5) Marriage is a reflection of God and His people. In the Old Testament, the people were Israel, in the New Testament, it is the church. As Paul wrote, this is a mystery.

What do you have to DO to be "married"?

Do you need to have a ceremony? No - the Bible never says that there must be a ceremony in order to be married in the eyes of God. Marriage is an life-long agreement between a man and a woman.

Do you need to be married by a minister? No - the Bible never says that.

Does marriage belong to the church? No - God created marriage to be a life-long agreement between a man and a woman and virtually all societies have had marriages of one sort or another. The Bible does not say that marriage belongs to the church.

What about traditions?

They are traditions - and some very nice ones, too. But they are only traditions. The wedding traditions of the ancient world were very different from our traditions today. But their marriages were just as much marriages then as ours are today. Nearly every society marks the beginning of a marriage with a ceremony or rite, but it is not necessary, except to our human minds.

God and His Word clearly tell us that marriage is designed to be for life. A man and a woman in a covenantal arrangement, with God as the witness.

The ESV

Archaic language has been brought to current usage and significant corrections have been made in the translation of key texts. But throughout, our goal has been to retain the depth of meaning and enduring language that have made their indelible mark on the English-speaking world and have defined the life and doctrine of the church over the last four centuries.

The ESV is based on the Masoretic text of the Hebrew Bible as found in Biblia Hebraica Stuttgartensia (2nd ed., 1983), and on the Greek text in the 1993 editions of the Greek New Testament (4th corrected ed.), published by the United Bible Societies (UBS), and Novum Testamentum Graece (27th ed.), edited by Nestle and Aland.

The currently renewed respect among Old Testament scholars for the Masoretic text is reflected in the ESV’s attempt, wherever possible, to translate difficult Hebrew passages as they stand in the Masoretic text rather than resorting to emendations or to finding an alternative reading in the ancient versions.

In exceptional, difficult cases, the Dead Sea Scrolls, the Septuagint, the Samaritan Pentateuch, the Syriac Peshitta, the Latin Vulgate, and other sources were consulted to shed possible light on the text, or, if necessary, to support a divergence from the Masoretic text. Similarly, in a few difficult cases in the New Testament, the ESV has followed a Greek text different from the text given preference in the UBS/Nestle-Aland 27th edition.

My daughter and I took a beginning Greek class and this was the one that the instructor told us was most faithful to the ancient text...