Difference between 'Preferred IUPAC Name' and 'Systematic IUPAC Name' When looking at different chemicals, I come across the 'preferred IUPAC name' and the 'systematic IUPAC name'. I've noticed that when I name chemicals, I name them by their 'systematic IUPAC name', as I've been taught to name them using this system. 

When is the 'preferred IUPAC name' used? I sometimes come across it when looking at aldehydes, ketones and carboxylic acids. However, the fact that it's 'preferred' makes me wonder whether chemists use this method more often than the other system.
The problem with systematic IUPAC names is that many compounds can have more than one systematic IUPAC name. A compound may be named correctly in two or more ways in accordance with the several methods recommended by IUPAC. Thus, asking for the systematic IUPAC name does not make sense for such compounds.

Therefore, current IUPAC recommendations (currently only for organic chemistry) include the definition of a preferred IUPAC name (PIN), which is the name preferred among two or more names generated from two or more IUPAC recommendations including also the many retained names.

Whether the preferred IUPAC name is also actually preferred by chemists cannot be generalized and depends strongly on the context.