What it means
The main versions are IEEE 802.3af (up to 15.4 W at the switch port), 802.3at, often called PoE+ (up to 30 W), and 802.3bt, which defines Type 3 (up to 60 W) and Type 4 (up to 90 W). The power that reaches the device is lower than the port figure because of cable losses. Standard Ethernet copper runs are limited to 100 m between switch and device.
Check the camera's maximum power draw, including heaters and IR illuminators, against the switch's power per port and its total power budget.
How it applies in India
On Indian highway gantries, the processing unit, switches and cameras usually sit in a roadside cabinet with a mains supply and backup, and PoE runs a short distance up the gantry. In hot climates, cabinet cooling and switch derating matter. Surge protection on both power and data lines is worth specifying, because lightning and unstable grid supply damage outdoor PoE equipment more than anything else.