Sentence:  Now we are liberal with our innermost secrets, spraying them into the public ether with a generosity our forebears could not have imagined. Where we once sent love letters in a sealed <WSD>envelope</WSD>, or stuck photographs of our children in a family album, now such private material is despatched to servers and clouds operated by people we don't know and will never meet. 
Meaning of the word marked with <WSD> tags:  A paper or cardboard wrapper used to enclose small, flat items, especially letters, for mailing.