Flat HDMI cables are exactly what they sound like. They are flat cables. They are especially useful when your DVD and satellite equipment are not right under your TV. They can run underneath the carpet easily and will not cause any kind of bubble or bulge in the carpet. Flat HDMI cables are just as good as regular HDMI cables, however they do cost a little more. Even online, they run about 2x the price of normal HDMI cables. Again, the main reason to buy a flat cable over a normal HDMI cable would be because you want to run it under the carpet or through a thin opening.
Another option is a thin or skinny HDMI cable. I prefer a skinny cable over a flat cable because you can fit it under (inside) your baseboards and above your carpet. You basically force into the space in-between and you have a hidden HDMI cable. This also means you don’t have to pull up the carpet and replace it. Usually thin HDMI cables are directional. This means one end goes in your DVD or satellite player and the other has to go into your TV or monitor device. It cannot go the other way. This is how the HDMI cable can be so thin. Normal HDMI cables are bi-directional and thicker. Again, these thin HDMI cables are more expensive than normal cables. The cheapest 30 foot thin HDMI cable I can find on Amazon is about $50.
Another reason to buy a thin HDMI cable is for travel. It is easier to store and takes up less space. They are great for connecting your notebook computer to a TV. It also can save you money as hotels charge a lot for pay-per-view.