That’s not one I’ve heard of before but from what I’ve been digging up on teh intarwebs it appears to be a rather particular form of Dispensationalism… maybe even Hyper-Dispensationalism.
Basic idea: The Jews were saved by the Kingdom Gospel - the Mosaic Law - which will find its fulfillment in the Millenial Kingdom of Christ. The Gentiles are saved by the Grace Gospel - the “ordinary” gospel.
It is somewhat like Marcionism in its idea that Israel is not the Church and that the Jews had a “seperate deal” with God, but it’s not in that it doesn’t believe (to my knowledge) that that separate deal is still in effect. The dispensation of Law has ended and the dispensation of Grace has begun.