From Safari help menu:
Some webpages display pop-up windows when you open or close the page. For example, a webpage might use a pop-up window to request login information from you or display advertising. You can block these pop-up windows.
Blocking pop-up windows stops only pop-up windows that open when you open or close a page. It does not block pop-up windows that open when you click a link.
To block pop-up windows, choose Block Pop-up Windows from the Safari menu so that a checkmark appears next to it.
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You can also choose Preferences from the Safari menu and click Security. Then click to select the "Block pop-up windows" checkbox.
If you block pop-up windows, you might miss important information for a webpage.
"I've always said that Pixar is the most technically advanced creative company; Apple is the most creatively advanced technical company"
-Apple CEO, Steve Jobs
http://www.fortune.com/fortune/technology/articles/0,15114,1025098,00.html - Apple CEO
http://www.pcmag.com/article2/0,1759,1572017,00.asp - Adobe CEO