I believe that you mean "Oyez Oyez Oyez" which is said in the begining of court trials. This phrase is synonymous with the opening "hear ye, hear ye", which is also used.
The phrase "hear ye" is in old english. The word "hear" is self-explanatory. However, "ye" is not a term widely used in English today. In Elizabethean English, and possibly before that as well. In old English, "you", which is just one word in modern English, into two terms: "thee" for singular (one person) and "ye" for plural (two or more people). An equivalent is, if you know French, the difference between "tu" (you, singular) and "vous" (you, plural).
Therefore, when "ye" is used, it is in reference to a group of people. For example, when talking to a class in the role of a teacher, you may say: "Ye shall finish thy homework" rather than "You will finish your homework" in comparison to when talking to a friend, where you may say: "I wish that I may accompany thee" rather than "I with that I may accompany (or go with) you."
Back to the question you asked. "Hear ye" basically means "you listen", but "you" means "all of you", since "ye" is used rather than "thee". So, the court bailiff is announcing: "All of you listen. The court is now in session and His Honour Judge Whoever is presiding." (It's longer in some places.)
If you are still confused or interested to find out further about the differences between old English and modern English, send me an e-mail at phoenixtears41@hotmail.com. I'll be happy to explain to you in more detail and you'll understand why, although old English seems more confusing, once you get used to it, it is actually clearer than modern English.
**Note: the source below tells of the synonymity of the phrases "hear ye" and "oyez"