An Anchor
Non-instructor help here. It is where the line you intend to cast is "anchored" to the water. It is this process of laying in or splashing / touching the water with your line that allows you to produce a respectable cast without the need to false cast, ( back cast ). Anchors vary from barely kissing the water to laying on the water possibly as long a couple seconds while you execute your cast. The closer your anchor is to your casting point, the easier it is to send on it's way. If your anchor is too close to your body, either your body or your gear is likely to get stuck by your fly. There is associated invaluble information available on this site from people who really know what they are talking about; certified instructors, videos and river sages.