Lat. 'In ones own proper person.' To represent ones self in court without assistance of an attorney, at least 'on the record.' Often shortened to 'in pro per.'
The U.S. Supreme Court observed in its unanimous decision in Kay v. Ehrler, 499 U.S. 432, that a lawmaking body may instead prefer to discourage attorneys from electing to appear in propria persona because such self-representation may often conflict with the general public and legislative policy favoring the effective and successful prosecution of meritorious claims. The high court observed that 'Even a skilled lawyer who represents himself is at a disadvantage in contested litigation. Ethical considerations may make it inappropriate for him to appear as a witness. He is deprived of the judgment of an independent third party in framing the theory of the case, evaluating alternative methods of presenting the evidence, cross-examining hostile witnesses, formulating legal arguments, and in making sure that reason, rather than emotion, dictates the proper tactical response to unforeseen developments in the courtroom. The adage that 'a lawyer who represents himself has a fool for a client' is the product of years of experience by seasoned litigators.. Id. at 437-438
An appearance may be in propria persona, and need not be by attorney.
Obs. 'In his own person.' It is a rule in pleading that pleas to the jurisdiction of the court must be pleaded in propria persona, because, if pleaded by attorney, they admit the jurisdiction, as an attorney is an officer of the court, and he is presumed to plead after having obtained leave, which admits the jurisdiction.
Also see 'pro se'