CFIDS stands for "chronic fatigue and immune dysfunction syndrome." It's an alternative name for chronic fatigue syndrome.
This name was never adopted by the whole medical community but was popular for a time with patients, advocates and a small number of doctors and researchers. It was preferred to the name "chronic fatigue syndrome" because many people believe the name trivializes the illness and they thought the term CFIDS was a more accurate characterization.
The name largely fell out of use in favor of ME/CFS or CFS/ME, with ME standing for either myalgic encephalomyelitis or myalgic encephalopathy. In the U.S., this name, like CFIDS, is largely used by the patient/advocate community and a few specialists.