Is it just a large church? Not according to Hartford Seminary researchers. To them, a megachurch has to be Protestant. And it has to meet these other criteria:
… strong charismatic senior ministers, many associate pastors, large staff, robust congregational identity that empowers 100’s to 1000’s of weekly volunteers, an identity that draws people from a very large area (sometimes an hour or more) and across parish boundaries, a multitude of programs and ministries organized and maintained by members, high levels of commitment and giving by members, seven-day-a-week activities at the church, contemporary worship, state of the art sound and projection systems, auxiliary support systems such as bookstores, coffee shops, etc. huge campuses of 30-100 acres, and other common megachurch characteristics.