Eberron setting material "fiends" play a central role, especially during the Age of Demons. References to "fiends" are almost always followed up by a reference to
Rakshasas, and obviously rakshasas play a more central role in
Eberron than they do in other D&D settings . However, does the term "fiends" refer to all evil outsiders;
rakshasas or some other grouping of evil beings?
Although the term is never defined specifically, the evidence provided tells us that, in
It can be inferred that, since the cosmology and planar structure of
"Fiend" in D&D 3.5 refers to any evil outsider.
The term is defined in the Monster Manual, under Types and Subtypes:
The only change in Eberron is that night hags are neutral outsiders rather than evil (Eberron Campaign Setting p. 305), and thus are not classified as fiends in that setting.
While certain creatures gain or lose the Extraplanar subtype in Eberron to account for differences in the planar cosmology (Eberron Campaign Settting p. 100), this doesn't actually change their type to or from Outsider, and so doesn't affect which creatures are considered fiends.