In high school, as part of the IB program(me), we had to take a class called Theory of Knowledge. As you might guess from the title, that’s an epistemology (study of knowledge) class. We talked about and tried to hammer out working definitions of lots of words relating to knowledge, among them, faith.
Among the dozen or so members of this class were several faiths, including Christian (Baptist, nondenominational and LDS), Muslim, Buddhist and I believe Hindu. (Sigh. I miss diversity.)
Anyway, the discussion on the definition of faith became interesting when I insisted that there is room in faith for doubt. Most people in the class, especially those very active in their religions (as I am), strenuously disagreed.
Today in church our lesson was on faith, and I finally (six years later) found the words to accurately explain what I meant.
Faith is not to have a perfect knowledge of things. It’s not to have a sure knowledge. Faith isn’t certain. (If you’re certain, which I do believe you can be when it comes to religion, then you know.)
However, faith has conviction. You believe something to be true, you hope for something to be true, but you do not know it. And even though you do not know, you act upon your faith (that is absolutely necessary for true faith).
But you don’t know. You don’t always know what might happen to you when you do the things that your faith requires of you. You may lose friends, you may “lose” 10% of your income, you may lose your life. You are uncertain because you don’t know what the consequences of your faithful actions might be. Ultimately, you do believe they’ll be good, but until you reach the final judgement, you might have to suffer every day for acting upon what you believe.
And you do it anyway.  You step out into the darkness, a few steps ahead of the light, believing and hoping the light will follow. Doubt might be too strong a word, but uncertainty isn’t.
Faith is acting with hope in the face of uncertainty.