The two videos above are from the article, "Local Teens Join Mormon Flash Mob." According to the article:
A flash mob is a large group of people who assemble in a public place to perform a spontaneous act and quickly disperse after it is over.You can trace the history of flash mobs over time at Wikipedia. This particular flash mob was part of a L.D.S. (Mormon) Youth Conference.
Youth Conferences are generally held once a year. They are usually a three day event or so, where spiritual, intellectual and social activities are sponsored by the Church for young people, usually ages 14-18. Events are usually held at college campuses during off-peak times.
This event occurred in California and about 350 teens were involved:
The teens were from a Church of Jesus Christ of Latter-day Saints youth conference. To kick off that event, they organized the flash mob to create a fun wholesome experience for themselves and onlookers, LDS spokeswoman Karen Lake said.I remember youth conferences as wonderful opportunities that were often spiritual pivotal points in my life and those of my friends. I have fond memories of them and whole-heartedly support them. It is just one of the things Mormons do for youth.