This question has intrigued many thinkers until today. Here, I tried to give you a witty definition. Read the following:
Who is a marketer? Somebody who keeps talking and feels that everybody would listen.
What is a product? A product is something that keeps talking and nobody listens.
Who is a brand builder? Somebody who keeps talking while others naturally feel that it is worth to listen.
What is a brand? A brand is something to which people are eager to listen even when it is not talking.