How do we define marriage?

Almost everywhere, marriage rates are falling, while people who do marry are tying the knot later in life than ever before. One Korean market research company has found that only 27.1% of respondents agreed that marriage is a must, while 40.1% disagreed with the statement.
Experts say this shift in opinion is not only due to people feeling financially unready to marry, along with other worries about the reality of modern married life, but also due to a changing perception of what marriage itself means. Of course, the marriage rate is falling also because people now simply take longer to settle down, and not necessarily because marriage has lost meaning. Is marriage still a necessary part of our lives, or is it becoming an unusual choice? Has the institution of marriage run past its expiration date?
This week, Shooters asks, "Is marriage outdated?"