I Am Reading My MRI Results For My Lumbar (talking

I am reading my MRI results for my lumbar (talking about L2-S1)and it says: there is loss of signal intensity, there is some ridging posteriorly at these three levels, there is also some mild ridging at L2-3 posteriorly and centrally?
There was more too it but, what I don't understand is what does: Signal intensity mean as well as ridging posteriorly and centrally?
could you please help me understand this?
Thanks,
Darla