What is meant by a sound marriage (nikah)? And what are the sound and invalid types of marriage?

A valid marriage (نكاح صحيح) is one that has fulfilled the conditions and pillars of marriage. As for an invalid marriage (نكاح فاسد), it is one that has lost a condition or a pillar, such as a marriage without witnesses or a guardian, or a temporary marriage (mut'ah), or a shighar marriage. Some scholars are of the opinion that there is no difference between what is invalid (فاسد) and what is void (باطل) in marriage, while others believe that an invalid (فاسد) marriage is one that has lost a disputed condition, and a void (باطل) marriage is one whose invalidity is agreed upon.