I assume you are talking about UCLA. All it means is that they have received your application and will review it before sending you a secondary. Most other schools do not do this and automatically send you a secondary as long as your stats are above a threshold (usually 500 mcat and 3.0 GPA). For UCLA they typically do a holistic screen (nobody knows their exact process), they look at your application and decide whether or not you get a secondary. I wouldn't think about it too hard, if you get a secondary, great, submit it.