A more thorough explanation:

Definition: Leave of court is when a judge gives permission to do something that is not part of the usual legal process.

For example, if a defendant is very upset by graphic autopsy photos, their lawyer might ask for leave of court to let the defendant leave the courtroom during that part of the trial.

This phrase is often shortened to just "leave."

Definition: Leave to sit is when a group within a larger group (like a committee) gets permission to meet while the larger group is also meeting.

For example, if a school board is having a meeting, they might give leave to sit to a committee that is working on a specific project. This means the committee can meet in a separate room while the school board meeting is happening.

Both of these phrases involve getting permission to do something that is not part of the usual process. They show that sometimes, in special circumstances, the rules can be bent a little bit to make things easier or more fair.