The etymology is interesting. The verb originally meant to 'burn' and the noun was a 'torch' or 'piece of burning wood' (think of 'firebrand'). Hence the concept of a 'branding iron' to mark who owned animals (and once slaves), as well as wooden containers such as barrels of wine. Later the word came to refer to a more general mark of distinction that did not need to be burnt onto someone or something. This could be positive or negative distinction. We have all heard the expression "he was branded a liar".
Today there are many definitions of what is meant by 'brand'. Here is how I Iike to define the word:
A collection of perceptions springing from people's total experience of a company, service, product or entity*. These perceptions give distinction, either creating or subtracting value.
* e.g. a country, city, place or person
In contrast I define a 'commodity' as follows:
Something that lacks distinction and perceived value so that (in a free market) it is at the mercy of price competition.
I say 'in a free market' because obviously where there is monopoly control a 'commodity' is not at the mercy of price competition.
I also believe that highly successful brands create there own different kind of 'monopoly': a monopoly in the minds of their customers and other stakeholders.