In INSPIRE, “refereed” means the article has appeared in a major, refereed journal and presents new results. A more detailed explanation is here. Conference papers are generally not considered “refereed”. A few journals always have either document type:conference paper or the toggle on for Refereed

Journals that are always considered Refereed:
Ann.Rev.Astron.Astrophys.
Astron.Astrophys.
Astron.Astrophys.Suppl.Ser.
Astron.J.
Astrophys.J.
Astrophys.J.Suppl.
Bull.Lebedev Phys.Inst.
JCAP
JHEP
Mon.Not.Roy.Astron.Soc.
Nature (Not including letters to the editor and news articles)
Nature Phys.
Nucl.Phys. B
Phys.Lett.
Phys.Rept.
Phys.Rev.
Phys.Rev.Lett.
Rev.Mod.Phys.
Science (Not including letters to the editor and news articles)

Journals that always have document type:conference paper and are not “Refereed”:
AIP Conf.Proc.
ASP Conf.Ser.
EPJ Web Conf.
Int.J.Mod.Phys.Conf.Ser.
J.Phys.Conf.Ser.
Nucl.Phys.Proc.Suppl.
PoS

There are a few very rare exceptions, e.g.

• some selected papers from IEEE conferences are sometimes published in the proceedings as well as in a regular peer-reviewed IEEE journal
• in the distant past papers from experimental collaborations sent to conferences were sometimes later published as regular journal articles

These exceptional papers get both document type:conference paper and Refereed.