From a multicultural point of view it is important to see how muslims might view this trend:
"The original meaning of the work nikah is the physical relationship between man and woman.
It is also used secondarily to refer to the contract of marriage, which makes that relationship lawful. Which of the two meanings is intended can be determined by the context in which it is used.
As for the definition of marriage in fiqh, the simple definition would go something like this:
"A contract that results in the two parties physically enjoying each other in the manner allowed by the Shari'a." Since this only focuses on one aspect of the marriage contract, Muhammad Abu Zahrah (a modern scholar) defines it like this:
"A contract that results in the man and woman living with each other and supporting each other within the limits of what has been laid down for them in terms of rights and obligations."
