I've not looked into the exact definition. My understanding of Unique Reputation is just the number of individuals you've received reputation from. You might receive reputation from the same person multiple times in different threads, but Unique Reputation only counts them once. It sort of shows the diversity of people you've helped or impacted positively.
Your total reputation score has more variation than that. For one, everyone starts with 10 reputation points for free.
The value of an individual thumbs up (+ to reputation) varies in a couple of ways. High reputation members, moderators and administrators have stronger thumbs as it were. Reviews and Articles--which any one can write--have more impact on your reputation as well when anyone gives you a thumbs up there. Thumbs up on posts in threads have the lowest impact.
Supporters are those who paid for a membership at the site to help support the site. Contact @Nicko for more information if you are interested in that.