Here's a rundown of Tulip I put together so that the matter can actually be discussed instead of people throwing tantrums about it
Total Depravity- Human nature is corrupted and cannot function as it did prior to the Fall without the assistance of grace. It is a more thorough rejection of the Pelagian heresy.
Unconditional Election- Before the foundation of the world, God predetermined how He would conduct His will which ultimately predestines His Elect to salvation through no condition wrought from other forces.
Limited Atonement- Also 'Particular Redemption', states that while Christ is sufficient to absolve the world, it is God's intent only to save the Elect.
Irresistible Grace- The Elect cannot ultimately resist the grace applied to them.
Perseverance of the Saints- A corollary of 'OSAS'. Salvation cannot be dismissed once given; if a person dies in apostasy, they were never thoroughly imbued with the knowledge of God in the first place.
This is the foundation of Imputed Righteousness in Calvinist belief, and the rejection of Infusion within Catholic ranks which dismisses salvation on account of mortal sin and renewal after penance.