I read every where that drive by download attack consists in downloading malware to the victim's PC and execute it without the victim's permission.  

My question: does this "download" term include downloading any given file (virus.exe, worm.js ...) ? Or does it consists only in a something like malicious JavaScript attacking vulnerable plug-ins or features of the victim's brower ?   

I ask this question because I did not find any article speaking about this.