It's a fairly new home recording standard for DVD discs (it's been around on movie DVDs for ages though). As you can see from the description, it allows for the storage of around 8Gb worth of data (compared to the 4.7Gb of single layer discs), and yes, you need a supported drive with special dual layer discs (which cost a fair bit).
I recommend the latest drives from either Pioneer (DVR-109) or NEC (ND-3520A).