Around the PLOTS website, you'll see small graphs that look like this:
These represent the amount of activity for a given project, or place -- that is, how much PLOTS community members have been posting notes -- research or documentation about that given topic, with the most recent activity to the right hand side. It is listed by week, and shows the past year of activity.
This display is called a "GitHub graph" because it was popularized by GitHub.com, where you can see contributions to a given open-source software project. Check it out at, for example: