Short hand for "as per Section 8" (or the people/places they apply to)
"As per section 8 of the US Army Regulation, this soldier is mentally unfit to serve and should be discharged." The soldier himself may be called a "Section 8 case" if he seems like the type to be discharged under the regulation. Like Klinger on M*A*S*H, he wanted to be kicked out of the Army under Section 8, hence all the cross-dressing.
"As per Section 8 of the US Housing Act," this section of the legislation deals with creating affordable housing for low-income individuals and how landlords can deem their properties 'Section 8,' and get government reimbursement for housing low-income tenants. The dwellings themselves are often called "Section 8 housing."
One term for two unrelated concepts; but both are uniquely American, best as I can tell.