There are many categories of "special needs" birds but in general this term implies that the bird needs to have some accomodations made in its environment to enable it to live an enriched and healthy life.
Impairments creating "special needs" can take both a physical and emotional form. Some examples are:
1) Physical deformities such as spinal malformations, paralysis, missing toes or legs, partial beaks
4) Emotional issues due to abuse or neglect resulting in phobic and negative behaviors including severe plucking and mutilation.
5) Medical issues requiring ongoing care (i.e. medications, wound management)