Points of Interest, or POIs, are locations in game that have some significance to players. It may be no more than a spot that is involved in a quest, but more often it is one of those places where you get big text across the top of your screen naming a particular area. Some locations also give Discovery Experience, and those locations are specifically listed in Category:EQ2 Discovery POIs.
NOTE: POIs are stored in the Objects database, and appear in the EQ2_Object: namespace. There is a flag that differentiates them from Resource Nodes and actual Objects. Unlike objects, which normally have a single location, and resources, which have thousands and none, POIs can display a location but that is only one location in the whole area that is the POI. Whenever possible, the location will be the entrance to the area, or the center of the area.
Quite often, the POIs by Zone category for that zone will have a map that shows all, or most, of the POIs in the zone, making it easier to see what they are near and how to get there.