In the sexual sense a fetish is delineated from a kink in that with a fetish it’s often considered necessary for attraction/sexual satisfaction to the haver. So strictly a person with a sadomasochism fetish can’t get off without receiving or administering pain, whereas a person with a sadomasochism kink will sexually enjoy it, but can also get off from vanilla sex.

But they’re often used interchangeably. Also within bdsm kinks can be nonsexual, with some folks not getting off on it, but still enjoying it.