On The Loose by Niall Horan speaks about a woman who is captivating and elusive, who catches the attention of everyone around her with her wild and free-spirited nature. The key themes include fascination with someone who is unattainable, the excitement and unpredictability of such a relationship, and the allure of freedom and spontaneity. Particularly poignant moments include the descriptive imagery of her carefree and entrancing behavior, and the realization that while she is thrilling, she is also unpredictable and not easily tied down.