The question seems to be stupid. We all know what a brand is. But if we quote a few definitions, there will be confusion.
A brand, by definition, is a short-hand description of a package of value, on which consumers can rely to be consistently the same or better over a period of time. A brand distinguishes a product or service from competitive offerings.
A brand is associated with a familiar logo. Whenever we come across this logo, we think of the brand and the whole value package it represents and the promises it carries. This is the way it is supposed to work.
A brand starts as a product and a name. But much can be built on that name.