Fetish
A sexual Fetish (or, more properly, a paraphilia) is getting turned on by something that isn't considered a normal turn-on by one's culture. Of course this means what is considered a fetish will vary, and puritanical cultures will even consider any form of arousal to be taboo. Anything that isn't a normal turn-on could be a fetish. That is the other reason not to go into a detailed description of what exactly a fetish is. In fiction, there are general clues to show what's being treated as a fetish—namely, how people react to someone being aroused by something. If people are either disgusted or uncomfortable talking about it, it's generally a fetish. If people are impressed, it's kinky, but still on the edge of normal. Handcuffs can easily slide between fetish and kinky this way.
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Just erotic, nothing kinky. It's the difference between using a feather and using a chicken.
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It's still uncommon to see a fetish openly discussed in mainstream fiction, and rare to see those with a fetish not treated like weirdos.
For a partial list of recognized fetishes, see That Other Wiki.
A Super-Trope to Casual Kink, Hemo-Erotic.
Compare Rule 34, Rule of Sexy, Fetish Fuel (when something in media sets off a viewer's fetish, while this trope is when someone on the show is turned on).
No real life examples, please; as mentioned on the Fetish Fuel page, everything is a fetish for somebody.