In anatomical terms, an afferent is a vessel or other conduit that brings substances towards a central area, which is often a major organ like the brain or the heart. It is the opposite of an efferent vessel, which carries substances away from these central locations.
The system of imperial units or the imperial system (also known as British Imperial) is the system of units first defined in the British Weights and Measures Act of 1824, which was later refined and reduced.
Imperial vs. Metric System. There are two main systems for measuring distances and weight, the Imperial System of Measurement and the Metric System of Measurement. Most countries use the Metric System, which uses the measuring units such as meters and grams and adds prefixes like kilo, milli and centi to count orders of magnitude. In the United States, we use the older Imperial system, where things are measured in feet, inches and pounds. It might be confusing if you are living in the U.S for the first time and are not used to this system.