well data includes everyting from browsing, watching movies, chatting, voice calls etc...and remember, watching videos consumes a lot of data..A 5 mins lenglthy video song will be around 15 to 20 MB depending on the quality of the video.So, if u r heavy youtube watcher then i suggest you to switch over to 500 plan and schedule your youtube wathing plans on free hours.Unlimited plans are also good but videos will buffer a lot.