The short answer is 'None'.
A cold pipe (aka Condenser) helps convert a material from the gas to liquid phase.
If you use it to collect vapours at a certain temperature from a boiling liquid it is called a Condenser.
If you use it to cause the Gas phase to become Liquid again (to stop it escaping) and drip back down to the boiling pot, it can be called a refluxing column.
If you do not cool it, and allow the vapour to continually heat the column, switch phase, mix with the other phase rising in the column, so that only the purest particles escape, you can call it a Fractionating column.