The most common tags on Mixcloud have a chart. This will display on a show as a number next to its tag(s).
Depending on how common the tag is, a chart can have between 10 and 100 entries.
During an upload's first week on Mixcloud an upload will make it into the chart if it has a lot of favorites, shares and listens (longer listens are worth more). These will all have more of an impact at the start of the week, so an uploader will need to keep the momentum up to stay in the chart.