A more thorough explanation:

Definition: A formula is a set form of words used in legal proceedings to identify the issue to be tried and the judgment to be given.

• Roman law: In Roman law, a formula was a written document prepared by a praetor and forwarded to a judex. It identified the issue to be tried and the judgment to be given by the judex. The formula was based on model pleas formulated by the praetor in his edict and adapted by him or other magistrates in civil suits for the benefit of the judex who had to try the issue.
• Common-law pleading: In common-law pleading, a formula was a set form of words used in judicial proceedings, such as those appearing in writs.

These examples illustrate how a formula is a set form of words used in legal proceedings to identify the issue to be tried and the judgment to be given. In Roman law, the formula was a written document that specified the relief sought against the defendant and the judgment to be given by the judex. In common-law pleading, the formula was a set form of words used in writs to identify the issue to be tried.