You mean overprovision surely
Indeed overprovision is the commonly used term although it makes poor English sense in this context!
Most SSDs are inherently overprovisioned by the manufacturer these days (more space is provided than exposed to the user)
The act of the user configuring less space by way of partitioning achieves an overprovision outcome but by giving less (underprovision!)
Im not actually sure how effective this would be in the face of wear levelling techniques and in any event you would need to be running your drive at near capacity.
