Cervical (neck)
Spondylotic (spine wearing out)
Myelopathy (spinal cord dysfunction)

This term describes a condition in the neck (cervical region) where the spine gets so degenerated (spondylosis, or the adjective form of the word is spondylotic) that there is impingement or squeezing of the spinal cord causing spinal cord dysfunction (myelopathy).

These views, through an unaffected area, C23, show how the spinal cord has plenty of room around it with the spinal fluid, which shows up white in this MRI sequence.

However, at the C34 area, which is more severely involved, shows no room for spinal fluid, as the spinal cord is compressed by the degenerative process. This patient at the time of presentation has severe spinal cord dysfunction.

Similar findings are seen at the C45 level as illustrated below, with a large herniated disc pushing right into the middle of the spinal cord.

Another condition that could cause spinal cord compression is OPLL:
Ossification (calcifying, or turning to bone) of Posterior Longitudinal Ligament

The Posterior Longitudinal Ligament (PLL) lines the back side of the vertebral body, and is at the front side of the spinal canal. This ligament rests right against the front part of the dura, which is the sac that contains the spinal fluid and the spinal cord.

In the diagram to the right, the PLL is illustrated by the purple line.

In these cross section views on MRI studies, the thick black line behind the vertebral bodies, which in this case is composed of calcified tissue, looks black on the MRI scan. The presence of the OPLL here contributes to the compression on the spinal cord. At the areas of compression, there is no white fluid around the spinal cord as there is above and below.

In the images below, which are from CT scans, the ligament tissue which has ossified (turned to bone) shows up white.

clinical significance of OPLL is that, while in most cases,

the spinal cord can be decompressed most directly from the front approach (as illustrated here), in cases with OPLL, usually the decompression has to be done from the backside, or what is called a posterior approach, such as with laminoplasty or laminectomy. The bony change of OPLL often causes the bone to become adherent to the dura (the sac containing the spinal fluid), so that operating from the front has a higher chance of having a spinal fluid leak.

Some symptoms go along with a cervical (neck) degeneration (wearing out) condition, like neck pain and numbness/tingling, but with spinal cord compression, the findings might be more subtle.
Often, patient with pure myelopathy (spinal cord compression, as distinct from nerve root compression) might not have much pain, but present more with balance problems and trouble with fine motor movements, like buttoning clothing, or opening a jar. On exam, there may be abnormal reflexes, balance, or other findings.

Myelopathy tends to be progressive and in most cases, a serious discussion of the options, in many cases including a discussion of surgical decompression, needs to occur.