People now recognize the term brand, but they generally associate brands only with companies and products. People are brands too, including you.
Let’s start with what is a brand. A brand is what people perceive of a company or product. It is a collection of experiences with that company or product that creates these perceptions. People use their experiences with you to create your brand. When you are speaking, you want to make sure you are you. You probably want to dress up, where a suit or nice dress, but make sure it is still you. If you pretend to be something or someone else, you are changing your brand. Look at Steve Jobs when he presented, he traditionally worn a black turtleneck and jeans. That was part of his image, not a suit & tie.