Race is a mostly an arbitrary social construct, so it means whatever someone wants it to mean. But normally it would represent a sufficiently distinct group by "blood" or genetics. Traditionally, of course, determined by simple gross appearance: hence the typical concept of white, black, Oriental, Indian, etc.
People might also use a much smaller scale and define Scandinavian separately from German or Hutu from Tutsi at the level of race: your typical nationalist would probably do things like talk about the "British race", but the concept is laughable with any awareness of the mixed nature of the people in any geographical area. Race generally is quite hard to really defend, although the above idea generally relating to skin/hair colour and some facial features is by now well embedded in our culture.
