From Jesse Morrell’s blog Biblical Truth Resources:
TULIP is the system of Calvinism. It is an acronym for their doctrines:
T: Total Depravity – the total inability of a sinner to repent and believe. No free will
U: Unconditional Election – In eternities past God chose a few for salvation (not because they repented and believed) and consequently chose most for damnation (not because they sinned). Eternal election and reprobation is not conditional upon what man does, but upon God’s eternal decree. Since man is totally incapable of choosing to repent and believe, God must choose who to give repentance to and who to keep in impenitence.
L: Limited Atonement – Jesus only died for those whom God elected for salvation. He did not die for everyone. If He died for everyone, they argue, everyone would be saved because the atonement is automatically and unconditionally saving in its nature.
I: Irresistible Grace – those whom God has chosen and for whom Christ died are drawn by the irresistible grace of God. They cannot help but to come to Christ.
P: Perseverance of the Saints – those whom God has unconditionally elected, who are automatically saved by the atonement, who are drawn by the irresistible grace of God, will necessarily persevere unto the end. They cannot help but to remain saved. If someone falls away from the faith, that means that they were never truly in the faith to begin with – they were never truly saved.