i don't really know if it's the correct definition but from what i know, fetish is something that is completely necessary for a person to truly enjoy sex or orgasm while kink is a preference. kink is also more "out of the norm", while fetish could be something we find in our everyday life.
I'm not entirely sure but I've always thought it was liking either an action or a physical trait. For example you have a pain kink or a foot fetish. Though they're probably pretty interlinked and have similar meanings.
what's the difference between kink and fetish btw?