What is the meaning of the word 'bin' in the context of RNA-Seq?
It's talking about things like "TSS_up_1kb", which is a "bin" of 1kb upstream of the gene. A bin is a somewhat generic term that in this context means "a region of some given size". Another example where you might see the term is with histograms. There, values are grouped into bins, with each bin then being represented by a separate bar in the graph.