BDSM This is an acronym for a conflation of paired terms, as follows: Bondage and Discipline, Dominance and Submission, Sadism and Masochism. For people seriously into these various pairs, the differences are important and the debates heated. Briefly, Dominance and Submission (D/s) is more about psychology, power exchange, and role playing. Sadist/Masochists consider themselves sensualists -- it's all about needing those physical feelings, or using them to get turned on. Bondage and discipline is just that, spankings to mummifications, with or without the S/M or D/s (note the dominant upper case "D" and the submissive lower case "s" -- the official affectation of D/s pundits). But on AFF, the preferred term is "kinky" -- which is considerably more inexact.
Bondage and Discipline sexphoto
Bondage - use of any sort of restraint in sex play. Although bondage can get elaborate with advanced sailor's knots, rope suspension and so forth, on this site, people generally mean the lighter varieties -- maybe a silk scarf around the wrists or a pair of handcuffs.
Sadism and Masochism
Cross-dressing sexphoto A member of one sex dresses as a member of the opposite sex. Drag queens and drag kings, for example. It would include the practices of transvestites who practice the behavior specifically for sexual arousal.
Dominant
Also dom, domme, domina and dominatrix -- the last three are female only. The person who wants to be the controlling partner or aggressor in sexual relations. It can also be used as a descriptor: "I am dominant in the bedroom." If the person has mentioned a D/s relationship or says they like it "kinky," it can mean playing the role of "Master" or Mistress" to the partner's "slave" or "servant." If someone says point blank, "I'm a dom (or domme)," they mean this type of role play, added, most likely, to elements like bondage, pain, and other goodies. Dominance/submission play. One person takes the controlling role in sexual activity, the other person takes the passive or obedient role. This "play" has varying degrees of intensity. In frequency it can range from once in a while to 24/7, and in intensity it can range from giving a few orders or deciding who takes what sexual position to inflicting severe pain.
Fetishes
Things other than erotic zones of the body that turn an individual on. Examples are rubber, leather, latex, fat, toes, boots, high-heels, sexphoto, corsets, nylons... That said, this narrow definition has come to incorporate BDSM, because people associated with BDSM practices often had a "fetish" for leather (whips, belts, straps, chaps, leather gloves, etc.). So a person who's into whipping might call that practice a fetish.
Kinky sexphoto
The narrowest definition refers to incorporating fetishes into sex play. You may find balloons give you a woody (balloon fetish), and so you (or your partner) rub your penis with a balloon to get you off. Broader definition includes BDSM. You like to be tied to the bed; your partner likes to be whipped; you like to worship your partner's arm pits, etc. However, on the site you will even broader definitions -- in fact it can merely mean "looking for sex that's more adventurous than what I'm used to. For example, if she's only had missionary sex with her husband for the past 20 years, she might think doing it doggie style is "kinky" -- or doing it outdoors, or doing it with three people. Many people think anal sex is "kinky."
Submissive A person who likes to take the passive role in sex or lets the partner give the orders and call the shots (also used as a descriptor). In the context of D/s play, the role takes on more requirements.