The word fetish is bandied about quite a bit. Someone with a lot of shoes is said to have a shoe fetish while someone who enjoys anal sex is said to have an anal fetish. However, this is using the term far too broadly.

Main Entry: fe·tish
Variant: also fe·tich /'fet-ish also 'fEt-/
Function: noun
: an object or bodily part whose real or fantasized presence is psychologically necessary for sexual gratification and that is an object of fixation to the extent that it may interfere with complete sexual expression
(Merriam-Webster's Medical Dictionary, © 2002 Merriam-Webster, Inc.)

A true fetish is something that is required in order for the person with the fetish to achieve sexual release. A person with a shoe fetish doesn’t just like shoes, he (and most of those with fetishes are men) must have a shoe or shoes present in some way during sexual relations in order to orgasm. An anal fetishist cannot come unless either her or her partner’s ass is involved.

True fetishes are considered paraphilias that may necessitate psychological intervention if experienced to a degree that causes undue anxiety or in some other way interferes with life. Certainly the majority of people who claim to have fetishes do not fall into this category.

“Fetish,” as commonly used could be defined as: an object or bodily part whose real or fantasized presence sexually arouses; a preference. A self-professed leather fetishist may enjoy wearing leather clothing, and the smell of the leather may arouse by triggering memories, but chances are she is able to get turned on with nary a cowhide in her presence.

Additionally, the terms fetish and kink have become conflated such that common understanding seems to be that every fetish is kinky and every kinky person has a fetish. However, these days preferring large-breasted women is hardly kinky, and liking one’s sex to be more than missionary-position-in-the-dark does not mean having a thing for lacy lingerie.

For more info: List of paraphilias; Kinsey Confidential Q&A:  Are Foot Fetishes Normal?