A fitting passage that describes grace is this:
For it is by grace you have been saved, through faith—and this is not from yourselves, it is the gift of God — not by works, so that no one can boast.
Here it says that grace is something by which salvation is effected. If you study the verb “save” in Greek, it means “to save, keep safe and sound, to rescue from danger or destruction”. It often times used to refer to healing, deliverance, etc. throughout the Gospels. Grace, then, is something that God gives, and that we appropriate by faith (as the passage points out) which results in being safe and sound from any type of destruction (in spirit, soul, or body). Grace can be thought of as God’s supply that’s been given nearly 2000 years ago through the finished work of Christ, and we appropriate and use it by placing active trust in it.
One way remember what NT grace stands for is this acrostic: GRACE: God’s Riches At Christ’s Expense. Also, throughout Paul’s writings grace (that which is given as a gift, outside of our merits) is often juxtaposed with works of the law (self-effort exerted in order to earn things from God). If we try to earn something from God in our own strength, it would give a reason to boast, since it would be an earned blessing. Grace leaves no room for boasting in self – only in Christ. The above-quoted passage from Ephesians also points to that.