Sprite rollovers sounds confusing, but an image sprite is just a collection of images put into a single image. For a web page with multiple images, it can reduce load time to contain them as an image sprite.
A sprite rollover is when an image changes it's state when you roll your mouse over the image. The original state and changed state are the two images you would save as one single image, the sprite. If you're still confused, you won't be by the end of this lesson!
View CSS Sprite Rollovers on Learn.co and start learning to code for free.