A more thorough explanation:

Definition: Litis contestatio is a Latin term used in Roman law to refer to the final agreement of the parties to a lawsuit on the formula the praetor would issue to the judex. It is also known as contestatio litis.

In simpler terms, litis contestatio is the point in a lawsuit where both parties agree on the issues to be referred to the judex (judge) and a document is issued to the judex by the praetor as his authority to act.

For example, in ancient Rome, if a plaintiff wanted to bring a lawsuit against a defendant, they would both appear before the praetor. The plaintiff would state the nature of their claim and ask for an action. If the praetor agreed, the parties would agree on the issues to be referred to the judex, and a document would be issued to the judex by the praetor as his authority to act. This ceremonial act of agreement between the parties and the praetor was the litis contestatio.

Another example of litis contestatio can be seen in modern-day court proceedings. When both parties have presented their arguments and evidence, and the judge has made a decision, the litis contestatio has occurred, and the case is considered closed.