In the United States, there is a wide variety of names used for the leader of a religious congregation. The name used depends on the group's tradition. When known, it is polite to use the term that's customary to the denomination itself. A "cleric" is an individual. A cleric is a member of "the clergy." The clergy is the collection of religious leaders within a single religious or denomination. It's used most commonly by people speaking about the Church of England (Episcopal Church in the United States). There isn't any single word I know of that means "all religious leaders of all religions." Neither is used in everyday speech in the U.S. and there isn't really any good substitute. One would never call Martin Luther King, Jr. "a cleric." The word "pastor" literally means "shepherd," a person who takes care of a flock of sheep. It is often used by Lutherans, Methodists, and "evangelicals." The word "minister" is short for "Minister of the Gospel." It is a common generic word for leaders of Protestant denominations, but is used less and less by specific denominations. The word "priest" is used for Roman Catholic leaders, and by more conservative congregations in the Church of England and the Episcopal Church of the US. "Rabbi" is used for leaders of Jewish congregations. That only begins to touch on the huge variety of use in the United States. Mormons have "Elders," Quakers have "Clerks of the Meeting," Muslims have "Imams," some churches have "no ordained clergy." (To illustrate common U.S. usage--and prejudice--there was a whole category of joke that began with the line, "A priest, a minister, and a rabbi..." I won't give an example because their point was perpetuate stereotypes about [Roman] Catholics, Protestants, and Jews--and, usually, to demean Jews by depicting them as sneaky tricksters. But you could never have a joke opening "Three clergymen walk into a bar...!")

A cleric is the leader of a religious organisation in any religion. A pastor is an ordained leader of a Christian church. The difference is in the religions. The cleric is for all religions, the pastor is all Christian.