This is not going to be easy, but basically...
Laced is a light feather with a dark edge right around.
Pencilled is a light feather with a dark shaft.
Barred is a light feather with one or more dark markings across the feather.
Unfortunately, in Poultry circles these terms have often taken on a misleading description. Some of the 'laced' breeds merely have a few laced contour feather on the saddle (back) or neck so don't take this too literally. Some of the 'pencilled' breeds have laced feathers with a few spots in the middle of the same feather.
The best examples of 'laced' are laced wyandotte hens. and 'barred' are barred rock hens.
The most misleading is the 'pencilling' which in the wyandotte is a lacing within a lacing.
Confusing, eh?