A spear-top fence finishes each vertical bar in a pointed cap that's hard or unpleasant to grab. The spear can be a forged decorative finial (heritage look) or a simple cut-and-welded pyramid (modern security look).
Spear tops are the standard anti-climb finish on commercial security fencing, school perimeters, and high-end residential boundaries. They also satisfy the AS1926.1 'no graspable top rail' rule for pool fences in most cases, since the top rail effectively disappears above the spear line.
Finial design matters for compliance and cost. Stamped pressed-metal spears are cheap but look it. Cast or forged spears (Cast Aluminium, Aurora Hardware) cost 5 to 10 times more per spear but read as architectural features.