The angular measure of the transverse section of a beam usually in the main lobe lying within directions corresponding to specified values of field strength relative to the maximum (e.g. half field strength beam width, half power beam width).
The beam width is usually measured in one or more specified planes containing the axis of the beam.
Please note that this is the term as it stands in the original IALA Dictionary edition (1970-1989)
acceleration due to gravity (m/s2)
International Association of Marine Aids to Navigation and Lighthouse Authorities - AISM