Definition - What does Wet Edge mean?
A wet edge is a wet painted area remains workable. This term is commonly used in the paint and coating industries.
The term is also used in decorative arts (faux finishing), and applies to the glazing process. The main consideration with painting trim (and walls) is keeping a wet edge to avoid any lap marks.
Corrosionpedia explains Wet Edge
When painting large surfaces, it is often necessary to connect the edge of a painted area which has been left for an appreciable time with a freshly painted area. When this can be done by blending this edge with free working paint without any lap showing, the film is said to present a wet edge. It is very important in many industries, especially the automotive industry.
If a wet edge is not maintained during painting, lap marks appear. When brushing or rolling, work should be done from the dry surface back into the wet paint, working fast enough to keep a wet edge.
The painter, while applying the paint, works in sections on a wall. The paint must not dry on the outer edge in order for it to be joined to the next section. If it does dry, the result is a "dry edge" that creates a line and can ruin the look of the faux finish.
To maintain a wet edge, an entire wall should be painted at once. Large areas like ceilings, extra-tall walls or stairwells cannot be covered in single, continuous strokes, so the best way to minimize lap marks on these areas is to feather out the paint along the edges. The thinner, feathered coat of paint avoids the buildup that causes lap marks. For the second coat, paint should be applied in the opposite direction. This crisscrossing paint application sharply reduces (if not eliminates) lap marks.