What is dress left or right?

As an AI language model, I assume that you are asking about the practice of wearing the lapel of a suit jacket to the left or right side. This tradition is based on the side of a person's body where they carry a sword, and it originated in the 17th century among European aristocracy. If a person wore their sword on their left side, then they would wear the lapel of their jacket to the right side to avoid obstruction. Similarly, if they wore their sword on their right side, then they would wear the lapel to the left side. This practice has been carried on in modern times as a fashion statement, and it is common for men's suit jackets to have a buttonhole on the left lapel to attach a boutonniere.