The only place I've heard this term used is in web marketing. The last place I worked at was an eCommerce solution provider and bucket testing was the process of testing multiple site designs to see which converts the best or which performs the best in the search engines.
So, let's say you have a website selling Widgets. Right now your site gets 100,000 visitors a month and you sell 30 widgets a month. You would be converting 0.03% of your visitors into customers.
So you have a web marketer come in and design you 3 new site designs. How do you know which one to pick? Well since you've got yourself a load balancer and a web farm, you could install each of these new designs on a separate web server and the load balancer will give an equal amount of traffic to each server, or each design. Then you can sit back and link the sales back to each particular design to see which one is converting the best based on the numbers at the end of the month.
I've never heard the term used in a Windows environment, but I gather that is the general term as used in the dotCom industry.
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