Kate Washburn didn’t know what to make of the email a friend sent to her office with the abbreviation “NSFW” written at the bottom. Then she clicked through the attached sideshow, titled “Awkward Family Photos.” It included shots of a family in furry “nude” suits and of another family alongside a male walrus in a revealing pose.

After looking up NSFW on NetLingo.com—a Web site that provides definitions of Internet and texting terms—she discovered what it stood for: “Not safe for work.”

“If...