Tagging is a trend on YouTube when someone make a particular type of video, usually answering a set of questions, and they then 'tag' other people to do it. It has been argued that the whole tagging phenomenon was started by YouTuber Alex Day, and even though similar question lists things were already happening on MySpace, Alex started them on YouTube.
The following are three tags I have participated in. The first is the lighthearted and seemingly random 'Toilet Tag'. The second is a tag stared by Alex Day (nerimon) about the past year. The third is a serous tag about women on YouTube.