Calvinism is a rare theology: It can be simply explained using a five-letter acronym. This set of religious principles is the work of John Calvin (1509-1564), a French church reformer who had a permanent influence on several branches of Protestantism.
Like Martin Luther before him, John Calvin broke from the Roman Catholic Church and based his theology on the Bible alone, not the Bible and tradition. After Calvin's death, his followers spread those beliefs throughout Europe and the American colonies.
The five points of Calvinism can be remembered using the acronym TULIP:
T - Total Depravity
Calvinism insists that God must do all the work, from choosing those who will be saved to sanctifying them throughout their lives until they die and go to heaven. Calvinists cite numerous Scripture verses supporting humanity's fallen and sinful nature, such as Mark 7:21-23, Romans 6:20, and 1 Corinthians 2:14.
U - Unconditional Election
God chooses who will be saved. Those people are called the Elect. God picks them based not on their personal character or seeing into the future, but out of his kindness and sovereign will.
Since some are chosen for salvation, others are not. Those not chosen are the damned, destined for eternity in hell.
L - Limited Atonement
I - Irresistible Grace
P - Perseverance of the Saints
The Elect cannot lose their salvation, Calvin said. Because salvation is the work of God the Father; Jesus Christ, the Savior; and the Holy Spirit, it cannot be thwarted.
Technically, however, it is God who perseveres, not the saints themselves. Calvin's doctrine of perseverance of the saints is in contrast to theology of Lutheranism and the Roman Catholic Church, which hold that people can lose their salvation.
(Sources: Calvinist Corner and RonRhodes.net.)