Mid-Acts dispensationalism (1) is a heretical theology that emphasizes an even greater distinction between the dispensations of law and grace than traditional dispensationalism, and holds that the Church is a distinct entity from Israel with different teachings and practices.
It holds that the apostle Paul's teachings are primarily directed to the Church, while the teachings of the other apostles are directed to Israel. They commonly only use the letters/books of the NT that they attribute to Paul and Luke. They believe that the Church began at a different point than the traditional Dispensationalism, usually at the start of Paul's ministry, and that the Church will be "raptured" before the end-times events, such as the Great Tribulation, occur. Mid-Acts Dispensationalism is considered as a more extreme version of dispensationalism.
Mid-Acts dispensationalism finds it's origins in Marcionism (2). It is to be noted that both mid-Acts dispensationalism and Marcionism are widely considered as heretical amongst even most dispensationalists.