The marabou jig is a plain lead head dressed with marabou - the soft, downy fibers from the base of turkey feathers. Wet marabou breathes: even when the jig hangs dead still, the fibers pulse and wave with the slightest current. That subtle motion is what panfish and trout key on, and it's why a marabou jig keeps catching when fish are cold and slow.
Most run in the 1-4 size range. White is the natural default and reads as a small baitfish or maggot in clear to stained water; olive and brown imitate sculpins and small minnows; black gives a hard silhouette in low light. The sweet spot is water from 40-60F in low to normal flow, when fish won't move far to eat.
The signature presentation is the jig hung under a bobber. Set the depth so the jig rides just above the fish, then do almost nothing - let the current and tiny rod-tip twitches make the marabou breathe. You can also swing or slow-roll it through a run, but the suspended dead-stick is the one that wins in winter. It is a staple for trout and winter steelhead holding in cold, slow tailouts.