"To suprême a citrus fruit is to remove the skin, pith, membranes, and seeds, and to separate its segments. Used as a noun, a suprême can be a wedge of citrus fruit prepared in this way."  Wikipedia

So this was all new to me when I took my Blade Master class at the local culinary school. I'd always admired those beautiful shimmering citrus segments with no extraneous membranes or other nasty bits, but I thought it was beyond my skill level to actually get them that way.  I was wrong.  Suprêming a citrus is actually very easy, once you get the hang of it, and, in fact, rather satisfying when you see...and taste the results.  Here's how you do it:

First, cut off the top and bottom of the citrus so that you
  can see the pulp, free of any skin, pith or membranes.
Next, cut down the sides of the fruit to remove the skin, pith and membrane, but not so deep that you lose a lot of the fruit.  You want to follow the shape of the citrus as you go,

Once the skin and pith are removed, hold the fruit above a bowl (so you don't lose any of the juice that is released as you cut out the suprêmes) and with a paring knife, cut along the membrane on top and bottom of each suprême to release the fruit.
When you're done, don't forget to squeeze the membranes in your hand to get the last of the juice.

Easy peezey lemon (or grapefruit) squeezey!