So you have an SD card. You lost some important things like photos or videos. SD data recovery is when you try to get these things back. It is, like searching the card for things that're still there but you cannot see them. When you delete something, it does not really disappear. The space where it was just gets marked as empty.
SD data recovery uses tools to find and fix these lost things. If you try to recover your SD data, you have a better chance of getting your things back. If you wait too long, it gets harder because the space where your things were might get used for something else. The condition of your SD card also matters. Read more: https://datarecovee.com/sd-card-recovery-software/