Faith

Now faith is the substance of things hoped for, the evidence of things not seen.
— Hebrews 11:1 NKJV
Now faith is the assurance of things hoped for, the conviction of things not seen.
— NASB
Now faith is confidence in what we hope for and assurance about what we do not see.
— NIV
Faith is the confidence that what we hope for will actually happen; it gives us assurance about things we cannot see.
— NLT
And without faith it is impossible to please God, because anyone who comes to Him must believe that He exists and that He rewards those who earnestly seek Him.
— Hebrews 11:6
So then faith comes by hearing, and hearing by the word of God.
— Romans 10:17 NKJV
You have become estranged from Christ, you who attempt to be justified by law; you have fallen from grace. For we through the Spirit eagerly wait for the hope of righteousness by faith. For in Christ Jesus neither circumcision nor uncircumcision avails anything, but faith working through love.
— Galations 5:4-6 NKJV

For me, faith is several things but most of all faith is manifested in, and measured by, trust. Trust in absolutely everything I know about God, His character and His promises. Trust in spite of all the problems and rotten things that happen. My trust has waxed and waned over the years with more waning than waxing. But that's really not smart; in fact just plain stupid. I know the truth and I know I can trust God 100%. Just do it, dummie.