Human Depravity
Human depravity is the universal condition of sin, moral corruption, and alienation from God. It means that people cannot save themselves or earn righteousness, but it does not mean that they are unable to understand or respond to the Gospel.
Expanded explanation
Human depravity means that every person needs God's mercy. Sin has corrupted humanity and alienated people from their Creator, leaving no one able to save himself or herself, earn righteousness, or repair that relationship through human effort.
This condition does not mean that people are incapable of understanding the Gospel, recognizing their need, or responding to God's call. It means that people are sinners who need the Gospel and cannot produce salvation from within themselves. God alone provides the saving work through Christ, but people are still responsible for whether they receive or reject the Gospel.
Context
Human depravity is related to Original Sin, but the terms are not identical. Original Sin describes the fallen condition and consequences inherited through humanity's connection to Adam. Human depravity describes the sinful condition expressed in each person's own life. People are not personally guilty merely because Adam sinned; they are accountable for their own sin and rebellion.
This distinction matters because the word depravity is sometimes used to move from the biblical claim that all people are sinners to the additional claim that no one can respond to the Gospel unless regenerated first. Decalvinised affirms the first claim without accepting the second. Human depravity explains why people need salvation; it does not establish that people are blind or unable to respond when God graciously calls through the Gospel.