What Does Lossy Mean?
Lossy is the opposite of lossless and it means that when a digital image is compressed, some of the image’s data and detail is lost.  JPEGs are a type of lossy compression, and whilst we can control how much a JPEG is compressed by when we save it, there is always a loss.  Sometimes the loss is imperceptible if we use high quality settings, but it’s there!
Additional Reading
- What Is A JPEG?
- What Does Lossless Mean?