When you urinate after having a full bladder your bladder should be completely empty after urinating.
But then your bladder can still have a bit of urine left in the bladder that may not make it out of your bladder but then that urine will be sent out of your bladder when your bladder fills up again.
So your bladder is usually almost completely empty when you urinate but there can still be a bit of urine left in your bladder which is normal.
If you have acute urinary retention it means that you cannot urinate at all even though the person has a full bladder.
If you have chronic urinary retention you can still urinate but won't be able to completely empty your bladder of urine.