A foreign group is a group not read by the usual (or default) means. It could be, for instance, a group from a different NNTP server, it could be a virtual group, or it could be your own personal mail group.
A foreign group (or any group, really) is specified by a
name and a select method. To take the
latter first, a select method is a list where the first element
says what back end to use (e.g. nntp,
nnspool, nnml) and the second element
is the server name. There may be additional elements
in the select method, where the value may have special meaning
for the back end in question.
One could say that a select method defines a virtual server—so we do just that (see Server Buffer).
The name of the group is the name the back end will recognize the group as.
For instance, the group ‘soc.motss’ on the
NNTP server ‘some.where.edu’ will have the name
‘soc.motss’
and select method (nntp "some.where.edu"). Gnus will
call this group ‘nntp+some.where.edu:soc.motss’, even
though the nntp back end just knows this group as
‘soc.motss’.
The different methods all have their peculiarities, of course.