24/7 slavery as a general term involves a submissive serving their Dom or Domme in a permanent capacity.
At an extreme level, this would involve the submissive living at the same place as the Dom and being in service at all times. On possibly a more common level, this could be done more remotely, with the submissive being on call all of the time, though the same concept of being in service to the Dom first and foremost would still apply.
Among Goreans, 24/7 slavery is called "lifestyle" (as opposed to BDSM-style "scenes" kept quite separate from one's daily life, or fantasy "roleplaying").
|This article based on an article 24/7 slavery from Kinkipedia on 13 Apr 2018.