Latin phrases pervade the legal profession; we see them in court opinions and in legal arguments. In many ways, latin phrases are a form of “shorthand” for lengthier concepts.
Here are some examples:
Sui Juris: In a legal complaint filing, it might say “Plaintiff, sui juris, resides at 123 Main Street.” Here, sui juris means “having full legal rights (meaning adult capacity, not under any disability).
Nunc Pro Tunc: A paper filed “nunc pro tunc” literally “now for then” is typically a filing made beyond legal time limits with an excuse. An appeal filed “nunc pro tunc” is offered as valid (though late) due to an excused circumstance.
Sua Sponte: This is a legal act taken “on its own initiative” without a pending motion or request. It is often an act by a Judge to swiftly effect justice when the circumstances dictate.
— BBC&B