An image optimizer is a tool or software that reduces the file size of an image while maintaining its quality. This is achieved by compressing the image, removing unnecessary metadata, and reducing the resolution. By optimizing images, website owners can speed up the loading time of their pages and reduce the amount of bandwidth required to display the images. Image optimizers can be used for various types of image formats, including JPEG, PNG, and GIF. Some common features of image optimizers include lossless compression, adjustable quality settings, bulk optimization for multiple images, and the ability to preview the optimized images before saving.