The term sounds like a single diagnosis, but it covers a few related problems of the lower spine.
What is lumbar disk disease?
Start with the parts. Wikipedia says: There is a disc between each of the vertebrae in the spine.
Those discs are what the disease name refers to, and the lumbar label places the problem in the lower back.
One common form
OrthoInfo (AAOS) describes the herniated disk. It says: A herniated disk happens when the soft, jelly-like center of the disk pushes through the tough outer ring.
That is one form, not a full list. How common it is, and how it compares with other disc problems, are questions for whoever evaluates you.
Next steps
If your symptoms match, the next choice is where to be evaluated. A reader in Little Falls should ask each office about visit fees and agreement terms before booking.
Three links help with background. WebMD's pain management center is a general guide. OrthoInfo's sciatica page covers leg symptoms. The American Academy of Pain Medicine explains what the specialty does.
A practitioner's note
A definition is cheap, and it is also where the decisions begin. Use it to ask better questions, then weigh each office on what it commits you to over time.