'Dot-com' is a buzz-word that the media love to use. It refers to an online business such as amazon.com, obviously originating from that .com at the end of URLs. There was a huge boom in dot-coms in early 2000. Investors were eager to back these ]projects], because after all, it's the Internet , so it must be good.
Things took a downturn when people realized that these companies were failing to make any profit. Panic ensued, shares were sold, many companies were brought to their knees. The papers decided to hop on the bandwagon aon the way down, and declared that it was all a total joke, really.
The dot-com crisis brought some much needed sense to the e-commerce industry. The crap sites paid the price (boo.com) whilst the best survived.

Go to fuckedcompany.com - and kick those dot-cons while they're down. (ha, ha.)