Alexa's traffic rankings are based on the usage patterns of Alexa Toolbar users and data collected from other, diverse sources over a rolling 3 month period.
Google Trends shows how often a particular search term is entered relative the total search volume across various regions of the world, and in various languages.
Multimedia refers to the all links that have been added to different social media websites such as wikipedia, stumbleupon, reddit, delicious, digg, etc.
