The title for this post probably doesn’t require a great deal of clarification, but just in case…
Chrome – This is an internet browser made by Google. Like Internet Explorer, Mozilla Firefox, Opera or even Safari. (There are others of course, but as people using them make up less than 2.5% of this site’s visitors, I’m happy to gloss over them for now).
Alexa Toolbar – This is some code that will tell you how popular a website is when you visit it. The lower the number, the better, so if your site had an Alexa ranking of 1, you would (theoretically) own the most visited site in the world. Until recently, only Internet Explorer and Firefox users had access to the official Alexa toolbar, and I believe it was only this one that actually registered visits to the sites you frequent, within Alexa’s system. (Other toolbars/extensions exist that will tell you the rank, but they do not tell Alexa to +1 to the number of visitors for a website on any given day.)
I should point out that some people (and anti-malware programs) will report this toolbar as something that needs to be removed. It does, after all, meet most definitions of spyware – a company records details of every site you visit. However, if you decide to locate the download, and then initiate the installation procedure yourself, I’m assuming you know what it does and are happy with this system.
Finally, many people make the argument that Alexa’s stats are not reliable (they only count people with the toolbar installed) and are easily gamed. So don’t go losing sleep if your site slips down in the rankings, or assume you’ll be able to sel your site for a 5 figure sum, just because you make it into the top 1000.