Thanks for using the forum. I am happy to address your questions, and my answer will be based on the information you provided here. Please make sure you recognize that this forum is for educational purposes only, and it does not substitute for a formal office visit with your doctor.
Without the ability to examine review your imaging I can not tell you the exact implications of the findings however I will try to provide you with some useful information.
The spinal column is made of levels: cervical (neck area), thoracic (upper back), lumbar (lower back), and sacral (lowest part of bones of spine). L5S1 means the lumbosacral area, the lower part of the back. The spinal cord is encased by bones called vertebra. These bones are separated by a substance called the intervertebral disc, commonly known as a "disc". This material may sort of be squished out from in between the two bones; this is called a herniated disc. When the herniated disc becomes separated from the rest of the disc, this is termed a sequestered disc. The disc may push on surrounding structures, namely the spinal cord and/or the nerves exiting from the spinal cord. Most often, it is the nerves that are pressed on, and not the spinal cord itself. Nerves start to form as they come off the spinal cord and exit through holes formed between the vertebra. This place where the nerve exits is called the neuroforaminal canal, and when a disc is protruding into this canal and pressing on the nerve, symptoms related to "radiculopathy" can occur.
In summary, the report means: there is a herniated disc at the lower lumbar level that is narrowing the place where nerves exit from the spine.
Thank you for this opportunity to answer your questions, I hope you find the information I have provided useful, good luck.