a failure to void urine due to obstruction, nervous contraction of the urethra, or absence of sensation of the desire to urinate

The inability to pass urine, even when the sensations are present to void. This can be acute and very painful or chronic and painless depending on the cause. Can be relieved with Self Intermittent Catheterisation (See relevant section)

Difficulty in initiation of urination or the inability to completely empty the bladder.

A condition where a person is unable to release urine from the bladder. Retention can be caused by obstruction of the urethra or atonic bladder.

In ability to empty urine from the bladder, which can be caused by atonic bladder or obstruction of the urethra.

The inability to empty the bladder. The patient may be unable to start to void (with no urine emptying from the bladder) or may start to void but be unable to completely empty the bladder. These patients often use catheters to empty the bladder. More about InterStim Therapy for Urinary Control. .