It shows, for the 96 hours (4days) before this post, how many accounts created transactions on the Blockchain that hour. The blue line is the first 48 hours, as reference, the red line the last 48 hours. It shows we are now at round and about 2,000 hourly active accounts Vs the 12,000 .. 18.000 of before the hard fork. So if this metric is any indication, still a long way from everything being irie.