Voluntary sterilization is when a person makes the decision to undergo a sterilizing procedure. For people with penises, this is usually a vasectomy. For people with ovaries, this is usually a tubal ligation.
More About Voluntary Sterilization
Voluntary sterilization can be a difficult topic to approach in a society that values the birth of children, especially for women and people with ovaries, and even more so if they don't have children. Many doctors still refuse the procedure for women under a certain age and/or without children.
Men generally face fewer barriers to voluntary sterilization, as the procedure is easier, more easily reversible, and fewer societal expectations of bearing and raising children.