A netbook is a small to medium sized, light-weight, low-cost, energy-efficient laptop, generally optimized for internet based services such as web browsing and e-mailing.
The form factor of a netbook is smaller than that of a notebook and they are very light in weight (usually 2 to 3 pounds). Common features include a small screen (usually around 7-inches to 10-inches diagonal), wireless connectivity, but no optical disc drive, and a smaller sized keyboard (usually 80 percent to 95 percent of normal size). There is also a trend of using solid-state drives instead of traditional hard disk drives. Netbooks typically include a pre-installed operating system, either a custom version of a GNU/Linux or Windows XP Home Edition.
The idea of a netbook is not new in 1997 HP introduced the OmniBook, now in 2008 HP is back with the Mini-Note, ASUS and ACER are others manufacturers which are fighting for this under $500 market-share. These low cost machines are good for students and people on the go that just need check emails, surf the net and edit quick documents.
I found a good video on YouTube promoting the new ASUS, enjoy:
