To me, there are two ways to look at this. Every person who practices a martial art is a "martial artist". However, many of us also recognize a philosophical construct that is also called a "martial artist".
So, yes, everyone who practices or studies a martial art is a martial artist. But there is a higher level, a set of standards, that many (especially among the TMA) hold as an ideal for martial artists. I assume this latter is what you're talking about, so that's what I'll address.
Among the ideals I hold for a martial artist:
- Humility
- A "student" approach (always looking to learn)
- A desire to develop life skills, not just fighting skills
- Enhanced self-protection by consciously avoiding unnecessary physical conflict
- Courage (a vague term)
- Submission of ego to learning and self-improvement
- Some focus on physical fitness - not necessarily athleticism, and this can mean a lot of things as we age
- A desire to learn lessons from MA that go beyond fighting and direct self-defense
- Honesty
- Integrity with a set of personal values
- Being open to other perspectives
I'm sure I could come up with more. Some will disagree with some of these, and that's not just okay - it's a good thing.