From LawGuru Wiki
Pro se is a Latin adjective meaning "for self", that is applied to someone who represents themselves without a lawyer in a court proceeding, whether as a defendant or a plaintiff and whether the matter is civil or criminal. Most courts allow people to appear in court and submit legal documents pro se, but some prohibit legal "persons" such as corporations from appearing without representation. Pro se litigants are usually able to obtain assistance from a pro se clerk, or in very limited circumstances, the judge may even give certain advice from the bench on how to navigate the law.
The decision to appear pro se may sometimes be one of necessity, given the cost of legal representation. Even indigent criminal defendants in jurisdictions that guarantee legal representation may still have to represent themselves in the later stages of appeal, as such representation is often only provided by the state during the initial trial. This is especially true in collateral proceedings such as habeas corpus or postconviction petitions that fall outside the normal appeals process.
Other pro se litigants may themselves be lawyers or have other legal experience, or simply be confident in their ability to convey their claim or defense without professional aid.
Jurisdictions that allow pro se appearances generally impose limitations on it for abuse or disruption, rather than granting it as an absolute right.
Also sometimes known as "propria persona" or "pro per". In England and Wales the phrase "Litigant in Person" is used.