Table 5.19 -- EDCS classifications whose label begins with O
| Label | Definition | Code |
| OASIS | A small, isolated, fertile, or green <TRACT> in a <DESERT_REGION> usually having a <WATERING_PLACE>; an oasis. | 795 |
| OBJECT | A person, place, thing, or concept; an object. | 796 |
| OBJECT_PROPERTY_SET | A <PROPERTY_SET> describing an <OBJECT>. | 797 |
| OBJECT_SET | A <SET> of <OBJECT>s. | 798 |
| OBSERVATION_STATION | A station that is equipped for observation and study. | 799 |
| OBSERVATORY | An <OBSERVATION_STATION> designed and equipped for making observations of astronomical, meteorological, or other natural phenomena; an observatory. | 800 |
| OCCLUDED_FRONT | A composite of two weather fronts formed as a <COLD_FRONT> overtakes a <WARM_FRONT> or a quasi-stationary front, resulting in a cold, warm, or neutral occlusion; an occluded front. | 801 |
| OCCUPATION_ZONE | A <REGION> temporarily held and controlled by a hostile military force; an occupation zone. | 802 |
| OCEAN | One of the major divisions of an expanse of salt <WATER> covering a <PLANETARY_SURFACE>; an ocean. | 803 |
| OCEAN_BASIN | A <TERRAIN_DEPRESSION> of an <OCEAN_FLOOR> approximately equidimensional in plan view and of variable extent; a basin. | 804 |
| OCEAN_FLOOR | The <WATER_BODY_FLOOR> of an <OCEAN>. | 805 |
| OFF_ROUTE_BEARING | The <DIRECTION> and distance from an <AID_TO_NAVIGATION> to a defined <WAYPOINT>; an off route bearing. | 806 |
| OFFSHORE_LOADING_FACILITY | A <FACILITY> located in a <WATER_BODY> for loading and unloading <CARGO>; an offshore loading facility. | 807 |
| OFFSHORE_PLATFORM | A <STRUCTURE> placed in a <WATER_BODY> and used: for production, loading, and discharge; as an <OBSERVATION_STATION>; or as a <SCIENCE_FACILITY>; an offshore platform. | 808 |
| OIL_BARRIER | A floating <BARRIER> to stop and contain oil flow on a <WATER_BODY_SURFACE>; an oil barrier. | 809 |
| OIL_DRILLING_RIG | A <RIG> assembled primarily for the purpose of drilling an oil <WELL>; an oil drilling rig. | 810 |
| OPEN_AIR_BATH | An open air bath. | 811 |
| OPEN_WATER | A <REGION> of a <WATER_BODY> where the <WATER> is flowing or free standing; open water. | 812 |
| OPERA_HOUSE | A <BUILDING> that houses a <THEATRE> designed chiefly for the performance of operas. | 813 |
| ORCHARD | A <TREED_TRACT> devoted to the cultivation of fruit or nut <TREE>s; an orchard. | 814 |
| ORE_REFINERY | An <INDUSTRIAL_WORKS> for purifying ores (for example: copper or silver) and extracting from them various metal and chemical products; an ore refinery. | 815 |
| OUTBUILDING | A small <BUILDING> that is separate from but is located near a main <BUILDING>; an outbuilding. | 816 |
| OVERFALL_REGION | A <REGION> of a <WATER_BODY> where short, breaking <WATER_WAVE>s are formed on the <WATER_BODY_SURFACE> when a strong <WATER_CURRENT> passes over a <SHOAL> or other submarine obstruction or meets a contrary <WATER_CURRENT> or <WIND>; an overfall region. | 817 |
| OVERHEAD_OBSTRUCTION | An overhead obstruction such as an underpass, an overhead <PIPELINE>, the overhang of a <BUILDING>, or other covered travelled way. | 818 |
| OVERPASS | A <BRIDGE> or <VIADUCT> used to provide clearance to traffic on a <TERRAIN_TRANSPORTATION_ROUTE> at a lower elevation; an overpass. | 819 |
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