A spigot-mount post slots into a steel sleeve that's been cast into the concrete slab. The post slides down over the sleeve and is fixed by a grub screw or wedge bolt at the base. Removing the post (for repair, refinish, or repositioning) is just a matter of releasing the grub screw and lifting it out.
Spigot mounts are common on stainless-steel pool fence and balustrade posts where the slab and the post arrive on different schedules. They're also useful for repair work: if a post gets damaged, you swap it for a new one in minutes without breaking up the slab.
The trade-off is that spigots add complexity and cost compared to a core-drilled or bolted post, and the grub-screw fixing is less rigid than a chemical anchor through a footplate.