纵容 means 'to indulge or connive at' bad behavior or wrongdoing — it always carries a negative judgment, implying the person should have stopped it. This is stronger than 宽容 (kuānróng 'to be tolerant/forgiving'), which is neutral or positive, and more active than 容忍 (rěnrěn 'to tolerate, put up with'), which is passive endurance. 放纵 (fàngzòng) is broader, covering self-indulgence and lack of restraint, while 纵容 specifically targets another's misconduct.