Consultant is one of those terms that have been assigned to me over the years that I have taken a while to get comfortable with. Like Web Designer (I'm not a designer) or Digital Strategist (I laughed when I first heard that term).
Don't ask me for my definition as I'm still working on it but I believe these characteristics need to be in play in order to be true to the word.
1. It should be about stuff you already know
Or at least is well within your comfort zone. Sure a bit of research or a little help from some friends along the way might be necessary, but if you're not confident you can provide the answer, find another problem (and refer the work to someone who can).
2. It should be about solving problems with a beginning, a middle and an end.
Whenever I've done consulting work I've always come to it with the view to making myself redundant in the organisation, at least on the problem I've been asked to solve. You might happily then take on the next problem, then the next, but if you can't confidently turn around at some point and say; "This problem has now gone away and you don't need me anymore", maybe you should just be on payroll.
3. All care. No responsibility.
This is a smart-arse thing to say but what it refers to is disinterestedness, not to be confused with uninterestedness. I'm always very interested in my client's problems. A client once told me I cared more about their organisation than most of their staff. But at the end of the day the problems belong to them. This detachment allows me to take an outsiders view and equips me better to solve the problem. And of course means I generally sleep better.
What do you think defines consulting?