Searching for "racket parallelism" does not really give anything relevant. In this case I searched for something that is extensively written about in the actual Racket documentation, both in the guide and reference material, so I know what I would expect.

It's a very natural search to do if you're thinking about parallelism and concurrency (both of which are suggested by Google, for example), but I assume most Racket users use the excellent documentation search for Racket. If you indexed that you'd probably get great results.