Web serving software uses Hypertext Transfer Protocol (HTTP) and HTTP status codes to record how Web pages and images are delivered to the Web surfer’s browser. For example, a 200 status code means the content of an entire Web page has loaded correctly.
Simply put, a meta refresh redirect is a method used by website developers to automatically send a visitor from one URL to another. As a result, the site’s log will record two page views (200 status codes) when the site visitor requests and sees only one page. Clearly not the way to do it if you’re the advertiser paying for impressions.
A 302 redirect, as the IAB glossary puts it, is "the process of a server sending a browser the location of a requested ad, rather than sending the ad itself." In other words, the 302 redirect is a temporary change in the URL of a page, so the browser simply goes to the location specified by the redirect.
In plain English, that means that a particular Web page can be designated — by Web serving software like Microsoft’s IIS or the Apache Web server — to automatically redirect a visitor to another page, without recording two 200 status codes in the logs.
Using software like Webtrends to analyze the logs of a site then allows webmasters to filter out certain HTTP status codes when running traffic reports. So by using a 302 redirect, a website can accurately and effectively report the traffic to its site separate from that of the ad server.
Due to its cache-busting nature, its ubiquity on the Net, and its trackability, the 302 redirect makes a solid standard for measuring Web traffic without including hits from ad impressions.