A more thorough explanation:

Simultaneous polygamy is the practice of having more than one spouse at the same time. It is also known as plural marriage. This is different from successive polygamy, which is the practice of having more than one spouse during one's lifetime, but not at the same time.

For example, in some cultures, it is acceptable for a man to have multiple wives at the same time. This is considered simultaneous polygamy. However, in other cultures, a man may have multiple wives over the course of his lifetime, but only one at a time. This is considered successive polygamy.

Simultaneous polygamy is illegal in many countries, including the United States. However, it is still practiced in some parts of the world.