I am following this tutorial which is very understandable for single-cell analysis. However, I am confused about only one concept in here which is 'complexity':
So to calculate the overall complexity of the gene expression, they divide nFeature_RNA to nCount_RNA. Also their cutoff for log10(nFeature_RNA/nCount_RNA) is >0.8. Also, for example in this tutorial complexity is "expressed genes per cell" https://broadinstitute.github.io/KrumlovSingleCellWorkshop2020/data-wrangling-scrnaseq-1.html
I searched a lot about complexity, I could not understand and I am confused. I would be grateful if someone could explain what feature/count shows exactly and why cutoff is 0.8. Also, why are these two complexity calculations are different, or are they the same definition actually?