A rollerball pen is a writing instrument that uses a water-based ink, which allows for smoother writing compared to traditional ballpoint pens. The ink flows more freely, providing a more fluid writing experience. Rollerball pens typically have a fine tip, making them ideal for detailed writing and drawing. These pens come in various styles and designs, often featuring a comfortable grip for extended use. Many people prefer rollerball pens for their vibrant ink colors and ease of use, making them popular choices for both everyday writing and professional settings.