Alexa.com is a website and a subsidiary company of Amazon.com that provides a wide range of services out of which one is Alexa rank. This rank is a metric that ranks websites in a particular order on the basis of their popularity and website traffic in the last three months.
Alexa generally considers the unique daily visitors and average page views over a period of 3 months to calculate the Alexa rank for a website. Alexa rank is updated daily. The lower the Alexa rank, the more popular a site will be. An increase or decrease in the rank shows how your SEO campaigns are doing.