What does it mean if I have urinary retention?

Can't urinate. Urinary retention means either complete inability to urinate, emergency which requires catheterization for relief, or else retaining significant amount of urine if urination is possible. Most commonly in older men with prostate enlargement, or women with vaginal or uterine prolapse or cystocele. Also caused by spinal cord injuries + other causes of neurogenic bladder, ms, some utis, urethral tic.
Incomplete voiding. That means your bladder is not emptying completely when you void. A bladder infection, some medications, surgery in the pelvis, diabetes, and spinal cord injury are some of the causes for urinary retention.
Depends. It means you are not emptying your bladder completely. This can sometimes lead to complete retention where you cannot empty your bladder at all. I recommend you see a urologist.