A publication of the US State Department that keeps track of the green card backlogs and informs us which "Priority Dates" are current so the applicants can expect to get through the last step of their green card processing. This is published every month around the 14th and tells us the availability for the following month. Note that certain categories of applicants ("immediate relatives") such as spouse of a US citizen are not shown in the visa bulletin because they are entitled to have their applications considered without any wait.