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1.
A feature of many web browsers that allows the user to prevent any data (like history, cookies, or the cache) from being stored while it is on. Also known as porn mode for really obvious reasons, but may be used whenever any sensitive/confidential information is going to be transmitted.

Private browsing is more comprehensive than simply erasing the history, because that's just a list of URLs, and browsers also save things like cookies (for sites to remember you) and images in the cache (to load faster later).

Private browsing is just a browser feature — there are other ways visited sites are tracked (for example, by your Internet provider), so it's not foolproof.
Say you are about to purchase a surprise for someone. If you choose a private browsing session, after you're done, other people won't see what gift you bought, or your credit card number, or your drug trafficking, or your porn.
by browserbrowsing July 18, 2010
 
2.
1) The button on Safari (Mac internet application) that keeps everything you do out of your history until you turn it off. Practically made for porn.

2) Jacking off

Thank Steve Jobs, everyone. Now you can watch porn and keep your history squeaky clean
1) Private browsing is a super invention

2) Woman: whatcha doin?
Man: Private browsing
by mac-lovin January 19, 2008