What is a trademark?

A trademark can be registered for any of the following:

A trademark can be Examples
An ordinary word Shell, Crown, Sunshine
An invented word Google, Toyota, Starbucks, Caltex, Coke, Microsoft, Kit Kat
A phrase 'Lonely Planet', 'Intel Inside'
Letters GE, BP, BMW, HP
Numerals 4711 (a perfume)
A person's name Tommy Hilfiger, Levi Strauss
Shape Qantas' flying kangaroo, a bottle of Coca-Cola, Shell's shell
Colour BP's distinctive green
Sound Intel's distinctive musical notes, MGM's lion's roar
Scent Eucalyptus Radiata scent for golf tees
Movement Mars's M&M character; Toyota's leaping person