CHS - Canadian Hydrographic Service - a Canadian government agency established in 1883 under the Department of Fisheries & Oceans that publishes and maintains nautical charts and publications for Canadian waters.
NGA - National Geospatial-Intelligence Agency - a United States government agency consolidated in 2003 from the National Imagery & Mapping Agency. Organized under the Department of Defense, the NGA provides both combat support and intelligence information. The NGA also maintains and publishes detailed worldwide nautical information, including sailing directions, port lists, and light lists for international transportation and naval navigation.
NIMA - National Imagery & Mapping Agency - a United States government agency established in 1996 to centralize responsibility for all US imagery and mapping. NIMA combined the DMA, the Central Imagery Office (CIO), and the Defense Dissemination Program Office (DDPO) in their entirety, and the mission and functions of the National Photographic Interpretation Center (NPIC). Also merged into NIMA were the imagery exploitation, dissemination, and processing elements of the Defense Intelligence Agency, National Reconnaissance Office, and the Defense Airborne Reconnaissance Office. NIMA was consolidated and renamed the National Geo-Spatial Intelligence Agency in 2003.
NOAA - National Oceanic & Atmospheric Administration - a United States government agency established in 1970 under the Department of Commerce, consolidating the US Coast & Geodedic Survey, the Weather Bureau, the Environmental Science Services Administration, and the Bureau of Commercial Fisheries. Among many other services, NOAA creates and maintains nautical charts and publications for U.S. coasts and the Great Lakes, providing over a thousand charts that cover 95,000 miles of shoreline and 3.4 million square nautical miles of waters.
UKHO - United Kingdom Hydrographic Office - a United Kingdom government agency under the Ministry of Defence that collects and supplies hydrographic and geospatial data for the Royal Navy and merchant shipping. The UKHO publishes and maintains British Admiralty maritime products and services, including nautical charts, sailing directions, and lists of navigation aids around the world.
Civil Ensign - the flag used by civilian vessels to denote nationality. It can be the same or different from the state ensign and the war ensign (or naval ensign). It's also known as the merchant ensign or merchant flag. Some countries have special civil ensigns for yachts, and even for specific yacht clubs, known as yacht ensigns.
Civil Flag - a version of the national flag that is flown by civilians on nongovernmental installations or craft. The use of civil flags was more common in the past to denote buildings or ships not manned by the military.
Courtesy Flag (or Courtesy Ensign) - a flag flown by a visiting ship in foreign waters as a token of respect. It is often a small (that is, smaller than the ship's own national ensign) national maritime flag of the host country, although there are countries (such as Malta) where the national, rather than the maritime flag is correct. The flag is customarily worn at the foremasthead of multi-masted vessels, the dockside yardarm or crosstree of the mast of single-masted vessels, while the house flag would be outboard. It may be flown from the jackstaff of vessels without masts.