A more thorough explanation:

Definition: A rule.

Example: The school has a regula that students must wear uniforms.

Explanation: This means that the school has a rule that requires students to wear uniforms. The term "regula" is used to refer to any kind of rule or regulation.

Definition: A general rule, especially of a court.

Example: The judge applied the regula generalis to the case.

Explanation: This means that the judge used a general rule of the court to make a decision in the case. The term "regula generalis" is used specifically to refer to a rule of a court.

Definition: A rule of pleading.

Example: The lawyer cited the regula placitandi in his argument.

Explanation: This means that the lawyer referred to a historical rule of pleading in his argument. The term "regula placitandi" is used specifically to refer to a rule of pleading.

Definition: The governing rule.

Example: The regula regulans determines how the court operates.

Explanation: This means that the regula regulans is the governing rule that determines how the court operates. The term "regula regulans" is used specifically to refer to the governing rule.