Some topics covered in Visa Bulletins from the United States Citizenship and Immigration Services website include the cutoff dates for immigrants waiting to come to the United States on a quota system, list of countries and the visa category/preference allocations. The Visa Bulletin contains charts and is available every month, as noted on USCIS.gov.
The Visa Bulletin, which is published by the U.S. Department of State, is a monthly updated waiting list that shows the availability of immigrant numbers for a given month. This list is also available on the USCIS website.
This list is useful because it shows the backlog in the different visa categories/preference allocations, which are family-sponsored, employment-based and diversity immigrants. For example, on an annual basis, the number of visas available for married children of U.S. citizens is approximately 23,000, as of 2015. If there are more visa applicants in this category in a year, they are placed on the waiting list according to priority dates.
The Visa Bulletin shows cutoff dates for each visa categories and subcategories. The priority date is the filing date on which the visa application was filed by either a family sponsor or employer. To get an immigrant visa number for a certain visa category from a given country listed, the filing date must fall before the listed cutoff date. The letter "C" on these lists stands for "Current" and means that there are visa numbers available for all eligible applicants, as noted by the U.S. Department of State.
On these lists, it also the shows the preference allocation. For example, under the family-based chart, there are different designations, such as F1, F2A and F3. The F3 designation stands for married children of U.S. citizens.