A more thorough explanation:

The Defense of Marriage Act (DOMA) was a federal law passed by the United States Congress in 1996. Its purpose was to define and protect the institution of marriage. DOMA specifically defined marriage as the union of one man and one woman, which allowed individual states to not recognize same-sex marriages that were performed and recognized under other states’ laws.

However, DOMA's sections were ruled unconstitutional by the United States Supreme Court in cases such as United States v. Windsor (2013) and Obergefell v. Hodges (2015). These rulings granted same-sex couples the constitutional right to marry and struck down the section of DOMA that allowed individual states to not recognize same-sex marriages performed in other states.

The implications of DOMA were that it denied many benefits and recognition to same-sex couples that opposite-sex couples enjoyed. These benefits included access to a spouse’s employment benefits, the recognition of the marriage itself, the rights of inheritance, joint tax returns and exemptions, and the right to cohabit together in a college or military housing.

One of the major provisions of this law was that a non-biological parent could not have a legal relationship with a child of the biological parent in a same-sex couple. Moreover, same-sex couples could not take medical leave to care for their partners or non-biological children. They also could not adopt children and during divorce proceedings, they could not petition the court for custody, visitation rights, or child support.

The supporters of DOMA believed that opposite-sex marriage was the only appropriate method for family formation and procreation. One of the major arguments from proponents of DOMA was that same-sex marriage could lead to alternative family formations and could even result in incestuous relationships and polygamous marriage. On the other hand, the opponents of DOMA claimed that DOMA’s definition of marriage as only between one man and one woman and other arguments were discriminatory on the basis of sex, and equated homosexuality with incest and polygamy.

Overall, DOMA was a controversial law that had significant implications for same-sex couples and their rights. Its eventual overturning by the Supreme Court was a major victory for the LGBTQ+ community and their fight for equality.