A word slipped out of a friend’s mouth the other day in front of his 10-year-old child. It was a word the child had never heard anyone say.

“Dad, what’s a landline?” the girl asked.

Within a decade, a staple of the American home for more than a century has been effectively wiped from the vocabulary of youth. Another one might be close behind: the remote control.

The television set has shone its flickering blue light in the homes of America since the 1950s, and it probably won’t be going the way of the 8-track anytime soon. But reliance on the TV is diminishing in the United States.

In May, Nielsen announced that for the first time in 20 years, the number of households that own television sets dropped, from 98.9 percent to 96.7 percent. Although the research firm said that some households shed televisions because of the recession — just as in the early ’90s — the company also noted that young people are growing more comfortable getting their television fix online.

For Palo Alto-based Monica Moreland, it was an easy decision. “It just seemed like so much time was wasted in front of the TV,” she said. She and her husband now turn to Hulu and Netflix, and “I do feel like we have more conversations and read more because of it.”

While television ownership has dropped, online video viewership has only increased. Last May marked an all-time high— 145 million online viewers in all. Cable companies and their content producers are trying to meet the demands for online content, but like the music, movie and journalism industries, are struggling to find the advertising dollars that would support big-budget television shows for small-budget advertising revenue online. Instead, many are attempting to create apps that will keep viewers engaged with their content throughout the day.

Starz severed ties earlier this month with Netflix after a three-year-long partnership, in part because it felt its brand was not getting enough credit for the arrangement. It may follow HBO’s example, which has taken a paywall approach with the HBOgo site. The online viewing channel and access to content though its iPhone/iPad app are only available to some cable television subscription owners, including Cox, Dish, Verizon and DirecTV users.

It’s been a huge hit for HBO, which announced last month that it would extend the service to more gadgets, including video game consoles, so that people can catch up on “True Blood” between stints of Wii Tennis. Contrary to the belief that giving up TV will cut back on hours watched, HBO said that viewers of HBOgo usually spend more time watching HBO content, probably because there’s no other channels to flip to inside the HBOgo experience.

One cable company that is not supporting HBOgo, Time Warner Cable, wants to create its own immersive experience, by challenging the idea that watching videos online is a separate experience from watching television on a set. A new ad campaign on Time Warner Cable channels advertises the TWCable TV app that lets people watch their favorite shows on any device. It’s a practice that started in 2006 with the Slingbox, a set-top device that beamed a person’s cable service to any device. The Slingbox never became a permanent fixture in homes despite its ability to send television literally anywhere , including to the iPad. Time Warner is hoping to teach that behavior to users.

Other cable companies have not ventured as far as Time Warner Cable. Apps offered by Comcast, Verizon Fios and Cox Cable allows users to control their DVR and view programming schedules remotely. But they can’t yet watch shows.

Remote controls may be in homes for a while longer, but they’re living on borrowed time.