Dataset Naming Convention

Hello, could you please help me understand the labelling for the dataset, for example:
How should I interpret:
kidney-instance-1-annotation-1 vs kidney-instance-2-annotation-1 vs tumor-instance-1-annotation-1

what does a) **instance** and b) **annotation** signify?

I tried vizualizing the files, but they all appear to be segmentations. Are there the raw input CT scans provided as well?