Yahoo! Inc. is an American global Internet services company. It operates an Internet portal and provides a full range of products and services including a search engine, the Yahoo! Directory and Yahoo! Mail. It was founded by Stanford graduate students Jerry Yang and David Filo in January of 1994 and incorporated on March 2, 1995. The company is headquartered in Sunnyvale, California. According to Web trends companies among others Alexa Internet and Netcraft, Yahoo! has been the most visited website on the Internet today with more than 412 million unique users.
 

Source: wikipedia.org

YouTube is a popular free video sharing website which lets users upload, view, and share video clips. Videos can be rated; the average rating and the number of times a video has been watched are both published.