A more thorough explanation:

sponsio judicialis (spon-shee-oh joo-dish-ee-ay-lis) is a term used in Roman law. It refers to a formal promise that a judge is entitled to acquire by virtue of their office.

For example, if a judge is presiding over a case and requires a witness to testify, the judge may ask the witness to make a sponsio judicialis to tell the truth. The witness would then promise to tell the truth under penalty of perjury.

Pl. sponsiones judiciales.

The term sponsio judicialis refers to a formal promise made by a person in a legal setting, usually in front of a judge. This promise is considered binding and carries legal consequences if it is broken. The example of a witness making a sponsio judicialis illustrates how this term is used in practice. By making this promise, the witness is legally obligated to tell the truth, and if they lie, they can be charged with perjury.