https://en.wikipedia.org/wiki/Dot-com_bubble
Literally...the...definition. Did you think it meant something other than that? Because it's quite literally in the word.
Most of the sites today were survivors of the era of easy venture capital, and they weren't any different than the other dotcoms. The whole point was the widespread adoption of the internet, thus...dotcom; because they all started up .com web addresses.
Google, Amazon, Ndivia, Ebay still dotcoms. Just survivors.
We still have remnants of their behavior too - with things like Uber and Lyft.