In the books, the Mord' Sith are women who have been trained since youth to be brutal torturers for the master of the land of D'Hara, the Lord Rahl. In their training they go through three stages. The first stage, they are tortured so they know and understand the pain they will be inflicting on others. In the second stage, the women are forced to watch their mothers raped and tortured. During the final stage, they must torture and kill their own fathers.
Mord' Sith have a unique weapon called an Agiel. It is a short rod that causes tremendous pain to anyone it touches. This is their instrument of torture and they know well how to use it. The Agiel that each Mord' Sith uses is the one that was used on them when they were trained. Even as a Mord' Sith is torturing someone and holding her Agiel, she is in pain.
Mord-Sith armour is composed of blood-red leather and is all-covering. Below are direct quotes from the series describing the attire of a Mord-Sith:
"She was sheathed in leather from neck to ground, cut to fit like a glove. Blood-red leather. The only deviation from the blood red of it was a yellow crescent and star across her stomach." WFR, entrance of Mistress Denna
"He could see that the back of her gloved hand was armoured, even the fingers. A bloodred leather rod, about a foot long, hung loosely from her wrist by an elegant gold chain." WFR
"...covered their shapely forms from ground to neck. A yellow star between the cusps of a crescent emblazoned the leather outfits at each woman's stomach." BotF, entrance of Cara, Raina, Hally, Berdine
"...covered from neck to toes in closely tailored bloodred leather displaying the yellow star and crescent of the Mord-Sith at their stomachs, carried their Agiel in fists swathed with armour-backed, red leather gloves." BotF
"...undoing the buttons running up the side of her ribs." BotF