Lateral recess
This is the area below the disc where the nerve runs more laterally towards the intervertebral foramen. Narrowing of the lateral recess is caused by facet arthrosis, usually in combination with hypertrophy of the ligamentum flavum and bulging of the disc.
From http://www.radiologyassistant.nl/data/bin/w440/a53f0b22de99d8_TEK-anatomy-6.jpg