Unique rep is the number of people who have given you reps.
Reputation received is the total number of thumbs you've received.
And reputation is based off of those two metrics. I saw my reputation go up by three points for one thumb. But there must be some other calculation involved because my rep is not simply 3x my rep received.
My guess is it has to do with who thumbs you. A bigger legend might hold more weight (in blood).