Overactive bladder (OAB) is a sudden, hard-to-control urge to urinate, usually with frequent urination, often waking you at night, and sometimes urge leakage. It comes from the bladder muscle contracting when it shouldn't — it is not a urinary tract infection, though symptoms can overlap.
It's common, more so with age and after menopause as estrogen falls, and it is treatable — first-line care is usually behavioural (bladder training, fluid and caffeine changes, pelvic floor exercises), then other options with a clinician. See overactive bladder.