ISO used to be fairly simple. In the film days, it was called ASA and was a measure of the sensitivity of that film to light. As we transitioned to digital and the years progressed, things have gotten a little more complex. In this video, the Syrp Lab team looks at ISO in the modern day. They take a look at features like Dual native ISO as well as discuss the issues around digital noise.
The video focuses on how ISO relates to video, as many modern ISO features are specifically designed for getting the best possible quality in your footage. But much of the information is still valid for photographers shooting still images, whether they be jpg or raw.