Question: What is a fixed-time marriage and what are its differences with permanent marriage?
Answer: The relation between man and woman becomes lawful by contracting marriage. There are two kinds of marriages:

1. Permanent marriage
2. Fixed-time marriage

In a permanent marriage, the period of matrimony is not fixed, and it is forever. The woman with whom such a marriage is concluded is called da'ima (i.e. a permanent wife).

In a fixed time marriage (Mut'ah), the period of matrimony is fixed, for example, matrimonial relation is contracted with a woman for an hour, or a day, or a month, or a year, or more. However, the period fixed for the marriage should not exceed the span of normal lives of the spouses, because in that case, the marriage will be treated as a permanent one. This sort of fixed time marriage is called Mut'ah or Sigha.

A woman with whom temporary marriage is contracted, is not entitled to share the conjugal bed of her husband, and does not inherit from him, and the husband, too, does not inherit from her.

However, if one or both lay down a condition regarding inheriting each other, such a stipulation is a matter of Ishkal as far as its validity is concerned, but even then, precaution should be exercised by putting it into effect.

Question: Can I marry a Christian girl for Mut'a or fixed time marriage?
Answer: If you are not married to a Muslim woman, you can marry her but you should obtain her father's permission, if she is virgin or dependent in the matters of her life.

ref.