A fetish is a sexualisation of a nonsexual thing / nonliving thing or not related to the genitals.
For example, you could have a "fetish" for high heeled shoes on your lady. Or thigh high boots. Or maybe you have a fetish for wearing women's panties. Or you could say that you have a foot fetish because feet really are not sexual.
Bending over and spreading your ass cheeks isn't a fetish. That would be more like a kink. Choking your partner would also be considered a sexual kink as well I would think. (That one is a little tougher to put a label on.)