Faith
Faith is a trusting response to God's revealed promise, expressed by believing in Jesus Christ and relying on him for salvation.
Expanded explanation
Faith is the means by which a person receives God's gracious promise of salvation. To believe in Christ is to trust him rather than rely on personal goodness, religious performance, or works. That makes faith necessary without making faith meritorious: the value is in the one trusted, not in the act of trusting.
God's initiative remains prior at every point. People do not discover salvation apart from God's revelation, the witness of the gospel, and the Spirit's work. The disagreement concerns what that grace does to the human response. Calvinism commonly says regeneration must occur first so that the elect person will believe. Decalvinised holds that God's gracious initiative genuinely enables a person to respond in faith, and that the response is meaningful precisely because it can be accepted or rejected.
Context
In the New Testament, faith is more than bare agreement with facts. It is trust in God's promise and reliance on Jesus Christ. Faith may be accompanied by repentance and obedience, but those responses should be distinguished from the basis of justification. The site therefore uses faith to describe a grace-enabled response, not a human contribution that completes God's work.