Augustine said, "What is faith, unless it is to believe what you cannot see." This is the obvious description, but scripture has quite a bit to say about what exactly faith is:
Definition of faith: Hebrews 11:1.
Faith is derived from the Word of God: Romans 10:17
Faith's demand: Hebrews 11:6
Faith's design: 2 Corinthians 5:7
The dualism of faith: Hebrews 4:2
Faith's duty: Romans 1:17 live by it.
Chicago: Moody Press, Divine Healing Today, by Richard Mayhue