A more thorough explanation:

countez (kawn-teez). [Law French] Hist. A direction given by a clerk of a court to a crier, after a jury was sworn, to count the jury members.

For example, in the past, when a jury was sworn in, the clerk of the court would say "countez" to the crier, who would then count the number of jury members present.

This term is no longer commonly used in modern English.

The term countez is a legal term that was used in the past to direct the crier to count the number of jury members present after they were sworn in. This was important to ensure that the correct number of jurors were present for the trial. The example given in the definition illustrates how the term was used in practice.