A Combo Box is a user interface element that combines a drop-down list with an editable text box. It allows users to either select an option from a predefined list or enter their own value. This feature is commonly used in forms and applications to save space while providing flexibility in data entry. Combo boxes are widely utilized in software development, particularly in programming languages like Java and C#. They enhance user experience by simplifying the selection process and reducing the likelihood of input errors, making them a popular choice in both desktop and web applications.