A paling is the same dressed timber board as a picket (65x19 to 88x19 DAR, treated pine or hardwood), fixed to the front face of horizontal rails the same way. The only difference is spacing: a paling fence sets the gap between boards to 0 mm, so the run reads as a solid screen with no daylight through it, where a picket fence keeps a visible gap, usually around 50 mm.
Paling fences are the standard timber boundary fence in Australian backyards, chosen over a picket layout whenever privacy matters more than the open, decorative look. The head can still be shaped (pointed, dog ear, round, French Gothic) or left flat, so a paling fence is not automatically plainer than a picket one; it is simply tighter spaced.
Because the boards sit tight, a paling fence needs a small amount of movement allowance built into the gap even at "zero," since dressed timber swells and shrinks with moisture. CAD60 refuses a gap between 0 and 5 mm for exactly this reason: it is either a true butted paling fence at 0 mm or a picket fence with real breathing room, never something too tight to nail, paint, or let the timber move.