A Meridian is a Great Circle line which passes through the poles of the earth. A local Meridian is one that passes through the observer's local position. The Greenwich Meridian passes through Greenwich, England, and is defined as having 0° Longitude.
Sector Lights is light emitted from a single position which will show up as either red, white or green depending on the angle of the observer, designed to indicate a safe navigational area.
Limb is when taking a sun or moon sight it is difficult to guess where the center is so the observer aligns either the top edge (Upper Limb) or more usually the bottom edge (Lower Limb) of the object on to the horizon. The sight is then corrected using the appropriate correction tables.
Running fix is advancing a LOP or previous line of position forward to a current line of position. A fix based on two separated bearings of the same fixed object and the distance run between the bearings.
Local Noon is the time when the sun reaches its highest altitude at your position and is directly north or south of you. it will then be at your Zenith and its GHA will correspond to your longitude.
Celestial sphere is an imaginary sphere with the earth at its center, on whose surface the stars, planets and other heavenly bodies appear to be situated.
Snellius construction is a method for combining three compass bearings to obtain a position fix, one where magnetic variation and deviation need not to be taken into account.
ITCZ, Intertropical Convergence Zone is the varying area of normally still air lying approximately between 5⁰ north and south of the equator.
The Estimated Position is the latitude and longitude at which the observer estimates his position to be, before fixing his actual position with the use of a sextant.