It's called FITSPINE and is used to stretch out your back by putting it on the floor and lying on it.
This is a description from a similar item on Amazon: “Back Backboard Stretch, Multi-Level Spine Stretcher for Relaxation, Posture Corrector, Decompression and Pain Relief for Neck, Shoulders and Sciatica”
It can be adjusted to three heights.
Can't verify it works as the person who bought it struggles to get up and down from the floor so they couldn’t use it.
Collect from Marshside
Back/spine stretcher board (Southport PR9)
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