Ecumenism:
Although the terms are often used together, "ecumenical" technically only concerns "Christian unity" while "interfaith" (or interreligious) concerns relations with non-Christian faiths. Judaism, however, holds a unique place, as we are the descendants of the Jewish faith tradition upon which Christianity was built and thus may consider our relations as “ecumenical.”
The search for Christian unity was one of the principal concerns of the Second Vatican Council. Vatican II published the “Ecumenical Directory" with the purpose of coordinating and developing the ecumenical efforts of the Church. The Catechism of the Catholic Church (1992 ed.) includes the ecumenical dimensions part of the basic teaching for all the faithful of the Church.
There are some misconceptions concerning ecumenism (and interreligious dialogue,) some unintentional, some deliberate. Ecumenical dialogue “implies speaking and listening, giving and receiving, mutual growth and enrichment. It is based on witness to one’s faith as well as openness to the religion of another. It is not a betrayal of the mission of the Church, nor is it a new method of conversion to Christianity.” (Pontifical Council for Interreligious Dialogue)
Jesus prayed, "That they all may be one." (Jn 17:21). The Second Vatican Council (“Vatican II”) directs the Church Faithful to this end.
Interreligious or Interreligious Dialogue:
This includes promoting respect, mutual understanding, and collaboration between Catholics and the followers of others religious traditions; encouraging the study of religions; promoting the formation of persons dedicated to dialogue.
Interfaith or Interfaith Dialogue
Similar to interreligious, often confused with “ecumenical.” Vatican documents prefer the term “interreligious.”
Building on learning, respect, discovery, and trust is a primary goal. The Church, therefore, exhorts her sons, that through dialogue and collaboration with the followers of other religions, carried out with prudence and love and in witness to the Christian faith and life, they recognize, preserve and promote the good things, spiritual and moral, as well as the socio-cultural values found among these men.” (Nostra Aetate 4.5)
Abrahamic:
Judaism, Islam, and Christianity are called “the Abrahamic religions” because they all share in their declaration of being descendants of Abraham.
Vatican II
The search for Christian unity was one of the principal concerns of the Second Vatican Council, commonly called “Vatican II,” and sometimes abbreviated just “V II” (1962–65). It was the 21st ecumenical council of the Roman Catholic Church, announced by Pope John XXIII on January 25, 1959, as a means of spiritual renewal for the church and as an occasion for Christians separated from Rome to join in a search for Christian unity. It is considered the seminal event of the Church in the last century and the birth of the modern Catholic Church. Many historians also consider it one of the most influential events in post-WWII world history.
Several major documents from the Vatican address Catholic followers’ moral responsibilities to advocate for Ecumenical and Interreligious efforts. (See “Resources” section.) The Catechism of the Catholic Church (1992 ed.) includes the ecumenical dimensions as part of the basic teaching for all the faithful of the Church.
Vatican II, affirmed John Paul II, "remains the fundamental event of the life of the contemporary Church; fundamental for the deepening of the richness given to them by Christ; fundamental for the (fruitful) contact with the contemporary world in a prospective of evangelization and of dialogue on every level with all men of attentive consciences" (24). ( Vatican Council II: Light for The Church and for The Modern World)