A more thorough explanation:

Civil union partners

Civil union partners are two people who are in a legal relationship that is similar to marriage. When a couple is in a civil union, they have rights to things like inheritance, employment benefits, property, and parental rights. The exact level of rights and responsibilities can vary depending on where the couple lives. For example, some places allow civil union partners to adopt children, while others do not.

Before same-sex marriage was legal in the United States, many same-sex couples entered into civil unions to gain legal recognition of their relationship. In some states, opposite-sex couples were also allowed to enter into civil unions instead of getting married.

For example, in Vermont, civil unions were available to both same-sex and opposite-sex couples starting in 2000. This allowed couples to have many of the same legal rights and protections as married couples, without actually getting married.

Now that same-sex marriage is legal in all states, civil unions are less common. However, some states still offer civil unions as an option for couples who do not want to get married.

For example, in Colorado, couples can choose to enter into a civil union instead of getting married. This gives them many of the same legal rights and protections as married couples, but without the religious or cultural significance of marriage.

These examples illustrate how civil union partners are two people who are in a legal relationship that is similar to marriage. They have rights and responsibilities that are similar to those of married couples, but the exact details can vary depending on where they live.