Raawr is a word commonly used to refer to the sound dinosaurs make. So technically seen it's an onomatopeia. It is nearly the same as 'rawr', the word it originally descended from, which is spelled with one 'a'. Raawr can have different definitions in Dinosaur; some examples below.
Raawr = 'I'm hungry'
Raawr = 'I love you'
Raawr = 'I eat you'
Raawr is not only used by dinosaurs, but also by really big cats and some boys and girls among us. It would not really be the same though, as when said by a dinosaur or a big kitty it might just be more intimidating. So don't worry too much about it if your girlfriend says 'raawr' to you. She's probably not hungry. But she might just eat you.