Supersessionism, also called replacement theology or fulfillment theology, is a Christian theological view
on the current status of the "church" in relation to the Jewish people and Judaism.
Supersessionism is the belief that the Christian Church has replaced the Israelites as God's chosen people and that the Mosaic covenant has been replaced or superseded by the New Covenant.
https://en.wikipedia.org/wiki/Supersessionism
Supersessionism is the traditional Christian belief that Christianity is the fulfillment of Biblical Judaism,
and therefore that Jews who deny that Jesus is the Jewish (DIVINE) Messiah fall short of their calling as God's Chosen people. Supersessionism, in its more radical form, maintains that the Jews are no longer considered to be God's Chosen people in any sense.
This understanding is generally termed "replacement theology." The traditional form of supersessionism does not theorize a replacement;
instead it argues that
Israel has been superseded only in the sense that the Church has been entrusted
with the fulfillment of the promises of which Jewish Israel is the trustee.
This belief has served not only as the explanation for why believers in Christ should not become Jews,
but is also the reason that Jews are not exempted by the Christian churches, from the call of the Gospel to believe in Jesus Christ for salvation from sin and from the penalties due to sin.
In recent times, the doctrine of supersessionism has been blamed for mistreatment of the Jews in the past.
Some liberal Protestant groups have therefore formally renounced supersessionism,
affirming that Jews and other non-Christians have a valid way to find God within their own faith,
which breaks from historic
Protestant teaching.
Dispensationalism affirms that salvation is only through faith in Christ, and that Jews fall short of obtaining the kingdom of the promised Messiah, unless they are converted to Christianity.
However, in their view,
a future mass conversion will result in the restoration of the nation Israel prior to the Millennium, apart from the church dispensation.
This anticipation of a future role for the ethnic and geo-political
nation of Israel in the plan of God,
apart from the Church, is what is meant by some dispensationalists who style themselves as rejectors of "supersessionism" or "replacement theology",
and thus they are using the terms in a way that is distinctive to their expectation of future events.
http://www.theopedia.com/supersessionism