Jimmy, that's the Fast Topics. Basically it's similar to what Altavista does with Prisma, or Exalead does at AOL France. It was introduced as a tool to refine searches. ATW used to show those on the serps, but stopped that sometime end of 2002. Topics are based on the taxonomy of the ODP, but don't completely reflect the ODP cats.
If you put Fast + Topics into site search you should find some discussions on the concept.