Buying a flat-screen TV can be daunting -- not only do you have settle on a brand and screen size, but you also have to choose a technology type. Head to any store that sells TVs, and you're likely to see a lot of LCD and LED TVs. But what is an LCD or LED TV? What does that mean, and why is it important?

What is an LCD TV?
The term "LCD" is an abbreviation, meaning "liquid crystal display." In contrast to the old tube-based televisions or shortly lived DLP TVs, LCD TVs offer a high-definition picture with a very thin screen, and have emerged as the dominant high-definition technology. In recent years, LCD TVs have accounted for almost 90% of the flat-screen market. Put simply, the vast majority of modern high-definition televisions you're likely to see in stores or in people's homes are LCD TVs.

But what about LED TVs? In reality, they're pretty much the same thing. That is to say, LED TVs are LCD TVs -- they just have an extra feature that older LCD TVs lacked. LED TVs, in contrast to older LCDs, have LED backlighting, leading to modest improvements in the picture quality.

A few years ago, this was a serious debate -- was it worth it to pay more for an LED TV? But at this point, TV manufacturers have basically abandoned standard LCD sets, replacing them almost entirely with LED models.

But LCD TVs aren't the only sort of high-definition TVs available -- there are also plasma screens, OLED sets, and projectors.

LCD vs. plasma
In general, plasma TVs offer better picture quality than LCD sets at comparable prices. Unfortunately, they tend to be a bit thicker and heavier, produce more heat, use more energy, and reflect more light compared with LCDs. Early plasmas also had a number of problems, including image retention (a still image left too long could burn into the screen permanently). Later plasmas solved many of these issues, but consumers continued to shy away.

As a result, Panasonic, one of the largest plasma TV makers, exited the business last year. Now there are only two companies that make them -- Samsung and LG -- and maybe not for much longer.

Both companies are betting on OLED, an emerging technology that promises far better picture quality than what plasma and LCD have offered. Samsung and LG have OLED TVs for sale right now, but don't expect to see them in many homes anytime soon. Samsung's 55-inch OLED retails for $9,000, while LG's competing model costs $10,000. What's notable about OLEDs is that they are curved -- Samsung and LG's TVs literally bend inward, forming a half-circle.

The curve might be more marketing stunt than design decision -- HDTVTest, reviewing Samsung's curved TV, noted that it could turn many buyers away. In time, I would expect flat OLED TVs to appear, but for now, if you come across a curved TV, know that it's an extremely high-end OLED.

LCD vs projector
The last alternative isn't so much a competing TV technology, as it is a different way to experience visual content. Projectors, compared with LCD TVs, offer a number of advantages and drawbacks.

On the plus side, projectors allow for enormous screens -- given a large enough room, a projector can output an image literally dozens of feet wide. They're also less expensive than LCDs TVs of similar quality. If you want a fantastic picture that's 100 inches or larger, going with a projector is by far the best bet.

But they do have their drawbacks -- namely, setup. A projector is not like an LCD TV in that you can just stick it in any room and plug it into the wall. Projectors require mounting, and a corresponding screen across the room. If you don't have the space for that, it's obviously not going to work, and if the room is bright, forget about it -- in order to see the picture, you need a dimly lit room.

LCDs are the standard
Because of the constraints, projectors are relatively uncommon -- most high-definition viewing is done on LCD screens. For the vast majority of TV manufacturers, that's all they produce. In fact, LCD TVs are so popular, the term has basically become synonymous with high-definition flat panels.

If you're in the market for a new TV, and you aren't willing to hunt down a plasma or pony up the cash for a high-end OLED, you'll be getting an LCD.

Sam Mattera has no position in any stocks mentioned. The Motley Fool recommends and owns shares of Apple, Google, and Netflix. Try any of our Foolish newsletter services free for 30 days. We Fools don't all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.