A spacer is any sapient who has primarily lived and worked in space throughout their lives, in contrast to a grounder.
Spacer culture is mostly made up of habits evolved from generations of space travel and living on ships. The acclimatization to that is what creates this. Spacer 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 multiple 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: the air circulation or water systems might have stopped working, for example.