In StarCraft, a Pylon is the Protoss energy structure required to power nearby buildings.
Protoss players normally must place Pylons before constructing most other structures. Each Pylon projects a visible power field, and buildings must be within that field to operate. Pylons also increase the Protoss player's available supply, making them essential to both infrastructure and army production.
The Nexus is the Protoss main base and resource structure, while the Gateway produces ground units. An Assimilator extracts vespene gas from a geyser. None of those buildings performs the Pylon's role of projecting the standard Protoss power field.
Pylon placement matters strategically because destroying a key Pylon can disable several nearby structures at once. Players therefore use Pylons not only for supply but also for forward vision, reinforcement points, and defensive layouts. The system is one of the clearest mechanical differences between Protoss construction and Terran or Zerg production.