| Term No. | Term Name | Term Description |
| 1623 | O horizon | Is an organic horizon formed or forming from an accumulation of organic material deposited on the surface, that is not saturated with water for more t..... |
| 4979 | Oasis effect | Vertical energy transfer from air to the crop; effect of dry fallow surrounds on the microclimate of a relatively small acreage of land where an air m..... |
| 5870 | Obelisk | An upright four-sided pillar, gradually tapering as it rises and terminating in a pyramid. It is ordinarily monolithic, used as a water diversion stru..... |
| 8232 | Object code | Machine language code produced by a translator program, such as an assembler, interpreter, or compiler. Instructions in object code can be executed by..... |
| 8233 | Object programme | The machine-language programme that is the final output of a coding system...... |
| 8645 | Objective function | Some rule for assessing, in an objective numerical manner the performance of the systems, using one or more chosen criteria in order to enable a compa..... |
| 9342 | Obligate Species | Species restricted to one particularly characteristic mode of life...... |
| 8947 | Oblique photograph | Photograph taken with a single-lens camera with the axis at an appreciable angle to the vertical, generally at 45o or more. A high oblique photograph ..... |
| 2307 | Oblique weir, or Skew weir | A weir with its crest inclined to the direction of flow as seen in the plan (illustrated)...... |
| 5132 | Observation well | A hole dug or augered into the ground for the purpose of observing fluctuations in the elevation of the groundwater table...... |
| 4187 | Observation well, Groundwater station, Monitor well, or Piezometer | 1 - A non-pumping well used for observing the elevation of the water table or the piezometric surface. 2 - Well used to watch for some anticipated, bu..... |
| 2786 | Obstruction weir type water seal | A water seal provided by a low weir (subsidiary dam) constructed downstream of the body wall (dam) (illustrated)...... |
| 3802 | Occupation crossing, Access, Accommodation | Crossing (bridge or culvert) that gives access between two portions of a farmer`s land. In Australia also called `access` or `accommodation`...... |
| 9136 | Occupier`s water rate, or Crop water rate | Water rate charged on the area actually irrigated and which usually varies with the nature of crop or crops, the quantity of water normally required b..... |
| 9343 | Ocean Conveyor Belt | The theoretical route by which water circulates around the entire global ocean, driven by wind and the thermohaline circulation...... |
| 7868 | Ocean flooding | Overflow onto lowlands by salt water, due to tidal action, storm surge or tsunamis, i.e. seismic sea waves. Land forms subject to ocean flooding inclu..... |
| 9344 | Ocean Ventilation | Downwelling of water from near the surface to the deep ocean. See also deepwater formation...... |
| 1295 | Oceanic | Inhabiting the sea where it is deeper than 200 metres...... |
| 8494 | ODBC | Open DataBase Connectivity, a standard for accessing different database systems. There are interfaces for Visual Basic, Visual C++, SQL and the ODBC d..... |
| 8234 | Off-line | 1 - Descriptive of a system and of the peripheral equipment or devices in a system in which the operation of peripheral equipment is not under the con..... |
| 8495 | Office, Microsoft Office | Microsoft’s bundles of productivity tools. Different versions contain some or all of Microsoft Word, Microsoft Excel, Powerpoint, Outlook, Microsoft..... |
| 6202 | Offset | The difference between the target value of the variable and the actual value...... |
| 3317 | Offtake canal | A canal that takes water from another canal...... |
| 3439 | Offtake regulator, Intake structure, Turnout, or Head of offtake | 1 - A structure built at the head of an offtaking branch or distributary channel to control and admit regulated supplies into it from the parent canal..... |
| 2747 | Ogee | A reversed curve shaped like an elongated letter `S`. The downstream faces of overflow dams are often made in this shape See `Ogee weir`...... |
