A D/s definition for you, who asked.

Domination and submission (also known as D&s, Ds or D/s) is a set of psychosexual behaviors, customs and rituals relating to the giving and accepting of dominance of one individual over another in an erotic or lifestyle context.

It is part of the BDSM group of paraphilias.
D/s is often referred to as the "mental" side of BDSM. Physical contact is not a necessity, and can even be conducted anonymously over telephone, email or (more recently) instant messaging services. In other cases it can be intensely physical, sometimes traversing into sadomasochism.

In D/s, one takes pleasure or erotic enjoyment out of either dominating or being dominated. Those who take the superior position are called Dominants, Doms (male) or Dommes (female), while those who take the subordinate position are called subs or submissives.

Submissives generally outnumber Dominants, with male subs outnumbering Dommes by the widest margin, often three to one or more.

D/s relationship styles
There can be any number of partners in a D/s relationship, with one Dominant sometimes having several subs, who may in turn dominate others. Relationships with multiple Dominants and a single submissive are rarer. The most common combination is a single Dominant and submissive couple, often in an ongoing committed relationship.

Romantic love is not necessarily a feature in D/s, partners might be very much in love or have no romantic relationship at all.

Variation in D/s (or BDSM for that matter) is virtually limitless and the activities take many forms, and may include servitude, verbal abuse, erotic humiliation, consensual slavery and sexual slavery and may be combined with other forms of BDSM in myriad combinations.

A classic example of D/s is the Sissymaid, where an adult male dresses in cartoonish female clothing and performs stereotypical female chores such as houscleaning or serving tea.

Some D/s relationships are sexual, others completely chaste.

Fantasy role play can also be a part, with partners taking classic dominant/submissive roles such as teacher/student, police officer/suspect or parent/child. Animal Play, where one partner takes the role of owner/caretaker and the other takes the part of a pet or animal, can also be D/s play.