Wikipedia to the rescue
“In common law, a next friend (Legal English prochein ami) is a person who represents another person who is under disability or otherwise unable to maintain a suit on his or her own behalf and who does not have a legal guardian. They are also known as litigation friends. When a relative who is next of kin acts as a next friend for a person, that person is sometimes instead described as the natural guardian of the person. A next friend has full power over the proceedings in the action as if he or she were an ordinary plaintiff, until a guardian or guardian ad litem is appointed in the case; but the next friend is entitled to present evidence only on the same basis as any other witness.”
“This disability often arises from minority, mental incapacity, or lack of access to counsel. Consequently, every application to the court on behalf of a minor, a mentally incapacitated person, or a person detained without access to an attorney, who does not have a legal guardian or someone authorized to act on his or her behalf with a power of attorney, must be made through a next friend (prochein ami, prochein amy, or proximus amicus). A minor frequently defends a suit not by a next friend but by a guardian ad litem, often appointed by the court with jurisdiction over the case or by a court with probate jurisdiction.
Some jurisdictions, such as the English civil and family courts, have recognized the right of mature minors to instruct solicitors and apply to the court on their own behalf since the 1990s.
Before the Married Women's Property Act 1882 in English Law and Irish Law (and similar acts during the same period in American law), it was usual for a married woman to sue by a next friend but that act, allowing a married woman to sue in all respects as a feme sole, has rendered a next friend unnecessary in the case of married women.”
