I define creativity as the process of having original ideas that have value. Creative work in any field often passes through typical phases. Sometimes what you end up with is not what you had in mind when you started. It's a dynamic process that often involves making new connections, crossing disciplines and using metaphors and analogies.
Creativity is about fresh thinking. It doesn't have to be new to the whole of humanity – though that's always a bonus – but certainly to the person whose work it is. Creativity also involves making critical judgments about whether what you're working on is any good, whether it's a theorem, a design or a poem.
There are various myths about creativity. One is that only special people are creative; another is that creativity is just about the arts; a third is that it's all to do with uninhibited "self-expression". None of these is true. On the contrary, everyone has creative capacities; creativity is possible in whatever you do, and it can require great discipline and many different skills.