Hi, welcome to HCM.
is outermost layer of intervertebral disc
. Nucleus pulposus
is inner most structure of disc.
In some cases inner part comes out through outer fibres known as annular tear. You are suffering from one of its type.
Anterolisthesis of L5 over S1 means there forward migration of lower most lumbar vertebra over upper sscral vertebra.
Hope I have answered your query.