Up
down" represents the negative z-value. The z-axis is the only axis that is not apparently arbitrary. The x and y values, "North", "South", "East", and "West" do in fact exist (and are named relative to the direction of the Earth's spin) but are not readily apparent.
A computer or machine is said to be up when it's working properly, and down when it isn't.
In baseball, a player is described as being up when he is facing the pitcher.
In rail transport, "up" is the traditional term for the direction leading to the terminus, i.e. towards milepost zero. For main lines in the UK, it refers to the direction of travel towards London. In Scotland, "up" is towards Edinburgh, and on the Valley Lines network in South Wales, "up" refers to services towards Cardiff Central.
See also: UP
