MHL is short for Mobile High-Definition Link, a new mobile audio/video interface standard--founded by Nokia, Samsung, Silicon Image, Sony, and Toshiba--for directly connecting portable devices, such as a smartphone or a tablet, to high-def displays. A supported device, such as the Samsung Galaxy II in the photo, can connect to any HDMI-ready HDTV via a cable and instantly mirror its content to the HDTV.
The content can be anything ranging from the device's home screen to videos, games, photos, and other media stored or streamed from the mobile device in high definition up to 1080p at 60Hz picture quality and 7.1-channel surround sound. The best thing about the MHL, compared with wireless display technology, such as WiDi or WHDI, is the fact that you can charge the phone at the same time and most importantly, MHL has a much broader support by major hardware vendors.
Many phones and TVs from HTC, Nokia, Samsung, Toshiba, and Sony currently on the market offer support for this standard now. Some devices can even have the support added via a firmware update.
When you have a phone and HDTV that supports MHL (most recent Android-based smartphones and TVs from the MHL Consortium-founding members do), all you need is an MHL cable to make the connection. One end of the cable is the same as a regular Micro-USB that fits into the phone charging/syncing port.
After that, the phone mirrors its content onto the big screen. This means you can play back movies, play games and music, and display photos that you would normally view on the phone's screen on the TV. There's basically no lag.
For a TV that doesn't have built-in support for MHL, the MHL-enabled portable device can still connect to it via a small adapter. Note, however, that some existing HDTVs can have support for MHL added via a firmware update. The Samsung UN46D7000 HDTV, for example, didn't support MHL when it first hit the market but its latest firmware will add the technology to the list of what it has to offer.
According to Tim Wong, president of the MHL Consortium, the MHL cable can be as long as 25 feet. However, it's likely that in the future, TVs will comes with a docking station for MHL-supported portable devices. This way, users can use the TV both as the extension of the phone as well as its charging station.