Prevenient Grace
Prevenient grace is God's gracious initiative before conversion. God does the initial work by revealing himself, providing the gospel, sending Christ, and calling people to respond. Decalvinised uses the term in this general sense rather than as a technical explanation that fallen humanity must first receive an additional grace before the gospel can be believed.
Expanded explanation
God always acts first. He created humanity, revealed himself, sent his Son, provided the atonement, and gave the gospel as the means by which he calls people to reconciliation. No one saves himself, and no one contributes merit to Christ's finished work.
Decalvinised affirms this general sense of prevenient grace. But the site does not affirm that humanity is totally unable to respond to the gospel and then require a second grace to overcome that inability. Our depravity makes us in need of the gospel; it does not make us blind to the gospel. The gospel is sufficient, faith is not a work, and people remain responsible to respond to God's gracious call.
Context
The phrase prevenient grace can obscure an important distinction. Many Arminian theologians affirm total depravity and use prevenient grace to explain how humans can get past that condition. Decalvinised does not affirm the Calvinist definition of total depravity in the first place, so it does not need to use prevenient grace as a way to restore an ability that total inability removed.
The relevant biblical questions are what God has already provided through revelation, Christ, the gospel, and the Spirit's witness; whether the gospel call is genuinely sufficient; and how faith can be a real human response without becoming a meritorious work. The term should describe God's priority without importing either the Calvinist or Arminian system into the discussion.