What is the "BEACON" and its symbol meaning from the Jeppesen Manual in the picture below? Does it just represent the beacon light? I'm confused.
In general, a beacon in aviation is defined by ICAO Annex 14 as follows:
Aeronautical beacon. An aeronautical ground light visible at all azimuths, either continuously or intermittently, to designate a particular point on the surface of the earth.
What you show in the Jeppesen charts legend is the aerodrome beacon. The little star on the right (above the airport symbol) indicates that this airport is equipped with such a beacon and the symbol on the left will show the exact location of this beacon on the airport ground chart (typically located on top of the tower). Here is an example at Perth, Australia (YPPH):
(chart: Jeppesen, picture: twitter.com)
Why is it called unidentified? Because there are also identification beacons that signal a morse code to identify them. Regular (unidentified) aerodrome beacons just show a regularly flashing or rotating light.
ICAO Annex 14 describes the details:
Aerodrome beacon. Aeronautical beacon used to indicate the location of an aerodrome from the air.
Identification beacon. An aeronautical beacon emitting a coded signal by means of which a particular point of reference can be identified.
126.96.36.199 An aerodrome beacon shall be provided at an aerodrome intended for use at night if one or more of the following conditions exist:
a) aircraft navigate predominantly by visual means;
b) reduced visibilities are frequent; or
c) it is difficult to locate the aerodrome from the air due to surrounding lights or terrain.
188.8.131.52 An identification beacon shall be provided at an aerodrome which is intended for use at night and cannot be easily identified from the air by other means.
Note that there is also another type of beacon, the hazard beacon:
Hazard beacon. An aeronautical beacon used to designate a danger to air navigation.
It uses this symbol on charts together with the altitude of the beacon: