From The RadioReference Wiki
A Site is the clustering of different towers locations in a given geographic area, with common frequencies and Talkgroups IDs common to a System, it may be all encompassing of an entire jurisdiction (2-12 towers) or a very small localized area (1 tower). It can also be inter-linked with other surrounding sites or stand by itself, either way its part of a System. The most problematic aspect for beginners to grasp is, in regular terminology "a site" is a singular location, i.e. a camp site. Where in the "scanner world" it means all towers collectively, inside 1 grouping with a common name, i.e. 1 group of 6 towers in the north is called the "North Site" or referred to as a "Simulcast Site." In the formal 2-way transceiver sense, these 6 towers make-up the "Site Cell" or "Cell Site"
For a specific Trunked Radio System, often Site Information is listed on an additional separate page for clarity, and to improve page-loading speed.