Maximum effective ISO is an estimate of the highest sensitivity at which a camera can capture excellent quality photos.
Cameras with higher effective ISO will be better choices for indoor photography, night shooting, and indoor sports photography, especially if you intend to make large prints.
You can learn more at our glossary entry.
Maximum effective ISO test data courtesy of DxO Mark.80D test data on DxO Mark D90 test data on DxO Mark
Very good image quality; Better RAW high ISO performance than predecessor; Improved buffer depth; Very fast AF; Dual Pixel CMOS AF is excellent; f/8 AF support; 1080/60p video; Headphone jack; Very good battery life.
New kit lens isn't very sharp; No 4K video; No clean HDMI out; 29:59 minute video recording limit; Phase detect AF not as sensitive in low-light as expected (Dual Pixel AF is better in low-light).