OpenEye names loosely correspond to the kinds of names familiar to a medicinal chemist. These names are intended to be a subset of the IUPAC 2005 standard's acceptable names, but not necessarily the PIN (Preferred IUPAC Name). These correspond to the types of names found in a Sigma-Aldrich catalogue or a Journal of Medicinal Chemistry article for example.
IUPAC names are intended to follow the IUPAC 2005 recommendations for the Preferred IUPAC Name (PIN). Unfortunately, this functionality is relatively recent, so the best that can be hoped for these names is that they are more IUPAC-like than the default OpenEye name style. Future release of Lexichem may further refine this definition to provide IUPAC2005, IUPAC93 and IUPAC79 name styles that reflect the corresponding standard's preferred name.
The Lexichem CAS name style is intended to follow the Chemical Abstracts Service's naming conventions, where they differ from IUPAC's. Once again, as this functionality is relatively recent, the effect is to generate names that are more CAS-like than the default OpenEye name style.
The Traditional name style corresponds to forms of compound naming that are now no longer acceptable to the IUPAC rules. The boundary between whether a trivial/common name is considered OpenEye or Traditional when it acceptable to IUPAC but not preferred is blurred, with OpenEye attempting to follow the more prevalent usage.
Finally, Systematic names correspond to the fully systematic IUPAC names that the IUPAC preferred names are slowly converging towards.