Potestas is a Latin term referring to authority or power. This term was an important concept in Roman law, and thus informed the legal systems of Europe after the collapse of the Roman Empire, because many new nations incorporated Roman legal concepts into their new laws. Eventually, the concept of potestas began to be replaced by other legal powers and authorities.
In Roman law, potestas came at varying levels, all of which involved absolute power over people subject to an individual's authority. The highest form was imperius, the power commanded by rulers and military commanders. These individuals had the power to issue edicts everyone had to comply with, or face potential legal consequences for disobedience. Magistrates also had a form of potestas they could use to compel compliance with legal verdicts and the law.
One of the most important forms of potestas was patria potestas, the power of the father. Under Roman law, all children, including adult children, were subject to the ultimate authority of their father unless he chose to specifically emancipate them. It was possible for this concept to cross generations, with a grandfather acting as the head of the family, and both his children and grandchildren subject to his authority.
When Roman woman married, they did so only with the consent of their fathers, and usually by arrangement between the heads of the two families involved. At marriage, the father could decide whether to turn the woman over to the command of her husband or his father, or to retain control over her, keeping her subject to his patria potestas. The Romans were far from the first or last culture to use such measures to control women, but it's notable that they also applied to men, unless their fathers chose to emancipate them.
Potestas also applied to the relationship between masters and their slaves. Roman slaves were subject to their owners or the fathers of their owners, although they could also be emancipated. Emancipated slaves were socially limited, unable to serve in the military or to run for public office, and they could win emancipation in a number of ways.
Many legal systems today recognize that adults should have full authority and autonomy over their lives, and this legal concept is outdated as a result. However, the concept of retaining authority over other people is still present in the legal relationship between children and their parents, and in cases where people with disabilities are deemed incapable of making decisions for themselves.