What the two columns mean
World rank is the university's QS World University Rankings position. Citations are the number of times work published by the university has been cited, as recorded in OpenAlex; it is the measure used to order universities that QS does not rank at all.
The two do not always agree. A large research university can out-cite a smaller one that sits above it in QS, because QS weighs reputation surveys and staff ratios as well as research.