Social Security Disability Insurance and Supplemental Security Income require that multiple elements be met before SSA will deem a claimant disabled. One of the steps in both programs is that the claimant has a severe impairment.
Listings are split into two main categories, Adult and Childhood Impairments. Within the two listings, impairments are broken down into areas of the body. Each area is categorized by number and actual impairments are listed in subcategory numbers.
Within that sub-category, SSA offers requirements to be met in order for the claimant to be determined disabled.
In my experience, medical providers do not always provide direct explanation of these listed requirements in medical notes when drafting routine medical charts. Social Security needs to be able to determine your Residual Functional Capacity before it knows if you meet the requirements for SSDI. Certain ailments require additional information from medical providers to the court. Medical Source statements can help with SSA and the ALJ with making a final determination.