The X axis is Principle Component 1, and the Y axis is Principle Component 2. The blog post I linked above describes what those terms mean in fairly simple terms. Both components represent genetic distance, in a 938-dimensional matrix, built from full genome analysis of 938 individuals, and reduced to two axes which are perpendicular to each other in that 938D space, and also maximize correlation between the visual distance in the graph and actual differences in the datasets. I realize that's a bit of a mouthful, but I don't think it can be simplified any further. Edit: I'll try anyway... Each point is a full genome (from a single person). The further two points are from each other, the more differences between the genomes. That goes for both X and Y. Both axes are composites of many different genes. The genes are selected such that there is as little overlap as possible between X and Y. This explanation is not quite as accurate as the above, but hopefully easier to understand. Here's a [PDF](https://files.catbox.moe/zs2qv7.pdf) of the full source article. The graph is actually not from the article itself, but from the supplementary data. Here's a full [PDF](https://files.catbox.moe/jea92k.pdf) of that. It's Figure S3 B.