This is a cumulative count of URL requests actually blocked by category policy. An admin watches the ratio of this to the total scanned-URL count as the headline web-filtering effectiveness metric, and a sudden jump in this ratio without any policy change usually means either a newly mass-blocked category was pushed or a categorization update reclassified a popular site the organization actually wants users to reach. For example, a block-rate jump right after a signature update reclassified a widely used business site into a blocked category, generating a flood of help-desk complaints.