A more thorough explanation:

An engagement slip is a note that a lawyer sends to a court to inform them that they are already committed to another court on a specific day and cannot appear before the first court as scheduled. This term is commonly used in Pennsylvania.

Lawyer John Smith has a case scheduled in Court A on Monday, but he is also scheduled to appear in Court B on the same day. He sends an engagement slip to Court A to inform them that he cannot appear on Monday because he is already committed to another court.

Another example is when a lawyer has a personal emergency or illness that prevents them from appearing in court. They can send an engagement slip to inform the court of their situation and request a new date for the hearing.

These examples illustrate how an engagement slip is used to inform the court of a lawyer's inability to appear on a scheduled date due to a prior commitment or unforeseen circumstances.