Falter means to hesitate, stumble, or waver, and everything from faith to voices can do it. So if you want to keep your bride or groom happy, it's best not to falter when it's your turn to say "I do."
Experts may falter if you ask them where falter came from, because the origins are pretty unclear. But everyone agrees on the current meaning: someone who falters is unsteady, wobbly, or unsure. You might falter while reciting a poem if you forget some of the lines, or falter crossing a rickety rope bridge when fear gets the most of you. But you certainly won't falter when someone asks you the meaning of this word.