A more thorough explanation:

Contestation of suit is a legal term used in ecclesiastical law. It refers to the point in a legal action when the defendant responds to the plaintiff's complaint. This response is called a plea and joinder of an issue. It is also known as litis contestatio.

For example, if a person sues another person for breach of contract, the defendant will respond to the plaintiff's complaint by filing a written answer. This answer will include any defenses the defendant may have, such as the plaintiff's failure to perform their obligations under the contract. Once the defendant files their answer, the case is said to be in contestation of suit.

Another example could be in a divorce case. If one spouse files for divorce, the other spouse will respond to the complaint by filing an answer. This answer may include any defenses the spouse may have, such as the lack of grounds for divorce. Once the answer is filed, the case is said to be in contestation of suit.

These examples illustrate how contestation of suit is the point in a legal action when the defendant responds to the plaintiff's complaint, and the case becomes contested. It is an important step in the legal process, as it sets the stage for the rest of the case.