A spacer is any sapient who has primarily lived and worked in space throughout their lives, in contrast to a grounder.

There is a Spacer "Culture". It is mostly made up of habits evolved from generations of space travel and living on ships. The acclimatization to that is what creates this.eSpacerr Culture is not to be confused with Exodan culture, although these two are similar. Spacer culture is more general and refers to habits usually held by more than species or that are common in multispecies crews.

Common foods are Red Coast bugs (originally Exodan) and Stasis stored vegetables of various kinds and origins.

Spacer instincts are very different to grounder instincts: To grounders, silence is a luxury. To Spacers, the absence of sound from the spaceship means something is wrong. (No footsteps bring heard through the walls might indicate trouble with the crew or neighbours, no sounds of pumps might be the air circulation or water systems, etc.

Ashby makes this very clear at the start of The long way to a small angry planet.