After weeks of plugging increasingly inviting discounts, retailers in the United States and several other countries are preparing for prime time: Black Friday, the bargain bonanza that still reigns as the unofficial kickoff of the holiday shopping season even if it's lost some luster.

Black Friday remains one of the busiest shopping days of the year, but its impact has been diluted by monthlong holiday sales and the convenience of buying online.

While most big U.S. retailers are closed on Thanksgiving Day, many will open early the following day — Black Friday, the unofficial start of the holiday gift-buying season and the biggest shopping day of the year.