What is a “lazy bladder? ”

Neurogenic bladder. "lazy bladder" is just a simple way to explain "neurogenic bladder". When the muscle of the bladder does not contract the way it should it will retain urine. Common in paralyzed patients or in peripheral neuropathies, diseases of the lower spine, neurological disorders, after stroke etc.
Infrequent urination. Subject only urinates once or twice a day. Usually have a very large bladder which is slow to empty. In children often caused by chronic suppression of urge to urinate. They have no neurologic defect, often do not empty bladder well & are subject to recurrent urinary infections. Some subjects with diabetes develop loss of sensation of bladder sensation which causes bladder to become overstretched.