What
According to wikipedia Femdom, or female dominance, refers to BDSM activities where the dominant partner is female. A female dominant is sometimes called a domme femdomme or domina. In the English speaking world, “Mistress” is by far the most common dominatrix title, while in most of continental Europe, the most common title is “Maitresse” or “Domina.” The most common dominatrix title in the Spanish language is “Ama.” The equivalent Japanese term is jo?sama, or queen.
Well that in itself is interesting but in my opinion like any aspect of BDSM what Femdom is, is open to many interpritations. There are also many catigories of “femdom” you may have come accross the terms lifestyle Domme, or Prodomme.
A Prodomme or professional dominatrix is usually a female Dominant who performs the top role in BDSM activities in exchange for a monetary fee. The play is negotiated with the submissive to fulfill their BDSM Femdom fantasy.
For the majority of professional dominants sex is not included in the session and therfor it is not an act of prostitution. In fact it is usually viewed by the Domina as a non sexual servive.
A lifestyle dominatrix may also be a Prodomme, but generally it is a term used to discribe a Dominant Woman is a dominatrix who practices femdom as a lifestyle, as opposed to a way of earning money.
Wikipedia also states that Femdom activities may draw on all areas of BDSM. Feminization and strap-on dildo play are common activities, as well as panty fetishism and boot worship.
Erotic humiliation can focus on the inadequacy of a male’s penis, demoting it to a plaything for the dominatrix, over which the male has no real control. Related femdom activities include ballbusting, cock and ball torture (CBT), verbal humiliation, forced chastity, orgasm denial or orgasm control, and forced homosexuality (in which a dominant female forces a heterosexual male to engage in homosexual acts for her amusement, or as part of feminization)
Many participants in this lifestyle conform to the Safe, sane and consensual and RACK models prevalent in the BDSM Community.
Light female domination scenarios may involve ageplay, erotic spanking, cunnilingus and body worship, especially foot worship and ass worship. More intense and heavier female domination scenarios may involve facesitting or smothering, which tend to focus on the sub giving the dominant female oral pleasure, or the dominant female performing anal sex on the sub using a strap-on dildo (see pegging). Other forms of more intense female domination can include face slapping, hair pulling, caning, heavy torture, dripping hot wax on the genitals and heavy whipping. For these purposes, note the issue of legal consent which may or may not represent a defense to criminal liability for any injuries caused.
In extreme scenarios, there is a focus on exchange of bodily fluids and total forfeit of rights from the slave (TPE), and acts may involve spitting domination or watersports (also known as golden showers).
A fairly common variation on this is a rape fantasy in which the female is the dominant partner, or wrestling/fighting in which the female is stronger than the male. These carry a similarity to forced feminization, where the sexual fantasy takes on an intellectual/emotional component, with men either trying to, or pretending to try to, take control, but failing.
So as you can see there is no simple definition for Femdom, and really the only thing that matters is how you see it 
I hope this page has answered some of your questions though.
You can find some interesting BDSM articles HERE at painspleasure
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