A common simple definition of “Grace” is unmerited favor.
This sweeps in two important dimensions. First, Grace is not a dealmaking exchange between two parties, specifically God (Christ) and us. To emphasize this point the adjective “free” is often appended to Grace–free Grace–but this actually misleads as to the meaning because Grace is itself “free,” and there is no such Grace that is “not free.”
The second dimension so the simple definition characterizes the nature of what is freely provided, namely “favor” or “kindness.”
The big issue as to the full meaning of Grace derives from a full understanding of the nature and extent of “favor” which God bestows and the true nature of “unmerited.”
An excellent diagnostic question–of ourselves and any other person claiming to be “Christian”–is to characterize in detail what they understand Grace to mean in these two aspects. An all-too-common-error stems from thinking that “favor” means God has given us ‘a chance’ to enter some state of forgiveness and bliss (often with more emphasis on the “bliss” than the “forgiveness”). And, continuing with consideration of such error, by our responding to this opportunity by some measure of independent self-initiative / self-determination, I arise to a state of being whereby “favor” is what happens. In such ‘theology,’ Grace is something that God gives a little initial push, to which we then respond in kind (or not), to which God then responds in kind to our response, and ‘the connection’ of Grace is made, either episodically or permanently. So, “favor” here means a multiplier that God provides to a small initiation on our part, coupled with that initial provisional step.
Another view of Grace derives from an acronym: G-R-A-C-E, God’s Riches At Christ’s Expense. Rightly understood, this can be a helpful reminder. But “riches” is not the so-called “prosperity Gospel.” And “expense” does not capture the eternal plan of the Father and Son to accomplish the miracle of redemption.
What follows below are several simple definitions. Following this is a link to more in depth lexical definitions. And following that are links to the occurrences of Grace in the NT.