When talking about the parts of a drainage system, the section of drain pipe between the drain outlet of a fixture and the trap serving it, is called the fixture outlet pipe.
Fixture outlet pipes are typically sized by the outlet of the fixture with some exceptions; for example, on a three compartment sink that is served by a single trap the fixture outlet pipe is increased one size. Some fixture outlet pipes may also be reduced from the size of the outlet of the fixture; for example, a shower base usually comes with a two inch outlet but only requires by code(in Canada) an 1-1/2" fixture outlet pipe.
The maximum length of a fixture outlet pipe is limited to 1200mm or four feet to prevent the velocity of the water draining from siphoning the trap. This length however does create the ability to place a trap for a fixture under the floor and is useful for island sinks and pedestal sinks.