html - What exactly link tag with rel dns-prefetch does? -


can explain in two, 3 words?

on websites straight after <head> saw several link tags attribute:

<link rel="dns-prefetch" href="http://www.googletagmanager.com" /> <link rel="dns-prefetch" href="http://www.google-analytics.com" /> <link rel="dns-prefetch" href="http://pagead2.googlesyndication.com" /> <link rel="dns-prefetch" href="http://googleads.g.doubleclick.net" />

what reason , "domains" should put href?


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