No it’s average weekend attendance. Yes many of the mega churches have more than 2000 at one service. But the trend is considered to include any of these “Christian” churches that have over 2000 weekend attendees. Pew, Hartford Institute and Wikipedia utilize this weekend definition. This definition has been in part due to many of the mega churches that originally have one large service dividing the services up and/or opening satellite locations and either replicating the main site’s sermon (or simply rebroadcasting it). The coworker I mentioned above attends “The Rock Church” in San Diego, but she physically goes to one of their satellite locations in a neighboring city where they broadcast the sermon from the main location in San Diego out to. She sees it live, but not in the same building or even city as the pastor.
Catholic Churches aren’t included because they’re not considered “Christian” (ie: read non-denominational, charismatic or Pentecostal (I hesitate to call them Protestant because they typically don’t consider themselves Protestant, more post-Protestant)). Regardless Catholic and Mainline Protestant churches, even the ones that do average over 2000 on a weekend, wouldn’t fit this classification.