What is this practice called?

The website Popurls(dot)com, just a basic news/content aggregation website, prefix's all their URL's with "popurls(dot)com/go/*ActualNewsArticleLink* "

So this way they are able to provide links and get credit for the traffic if they were to link to it. What is this "redirect" practice called?

Source: http://en.wikipedia.org/wiki/PopUrls

" the site created a new trend in the so-called Single Page Aggregators and serves as a case study for Web Syndication."

I understand that the site is a news aggregator but not all news aggregates use that type of prefixed linking. It appears FARK and POPURLS does however Reddit doesnt add a prefix to the link like these other ones do.

Scroll your mouse over a link on either of those pages and see that the link to the article is prefixed with Fark(dot)com/goto/*articlelink* and popurl does the same.

Is this is some php script?

It's called "click tracking".