Every tag members have put on a release, drawn as a constellation. A tag is a circle, as large as the number of releases carrying it, and two tags are joined when they describe the same records: the stronger the line, the larger the share they agree on. So the picture shows not what is popular but what belongs together, and it changes as you tag. Browse the vocabulary on the tags page.
Pick a tag (click a mark, use the arrow keys, or choose a table row) to see what it is most often assigned alongside.