Wanderers are a technical 'race' within the Microcosm, composed of sapient aliens whose individual populations number no more than 10,000. Existing populations that decrease below the threshold are not 'demoted' to Wanderer status.
Wanderers are typically members of distant civilisations, having travelled for many centuries in cryosleep. Since the Millennium Signal was first broadcast through sub-resonant quantum communication frequencies, intergalactic migration has decreased