What is Alexa.com

[nighthawk]

I want to sign up for ppc ads with a company that says that my site must be at least 1 month old and it must have some traffic according to Alexa.com. Are they some sort of spies? How do they now how much traffic my website has?

[webmaster]

Alexa.com keeps track of websites using a free toolbar. The estimate the traffic of sites using the stats they get from the users using their toolbar. It's a bad system because not many people use the alexa toolbar. Just download it and use it yourself when you click around on your site, and you will get a better alexa rank.

[celeron8]

its site to rank sites depending on traffic , to know if site is good ,its should be submitted there

[michaelhoffman]

It is a websites which gives details on traffic levels for the websites. Alexa then tracks where you go and compiles the information into rankings based on the number of hits to each site. Depending on how many viewers have visit a website, the Alexa rank is measured.

[steveoracle]

from Wiki, good explanation:

http://en.wikipedia.org/wiki/Alexa_Internet

Ste