Kelpie was a magnificent black mare originally owned by a man named Hotspurn. After his death, the mare became Ciri's mount. Although Hotspurn had never named the mare declaring that it was silly to name animals, Ciri named her Kelpie. The name came from Ciri's first sighting of the mare and Hotspurn crossing a river. The girl was immediately smitten with the mare. Ciri's choice of name for the horse greatly amused Vysogota.
Kelpie could be summoned by rubbing a magical bracelet. This was particularly helpful when Hotspurn died as the mare had been set away to lead the brigands astray.
During Wandering in the Dark quest at one point in order to find their way out of the dungeon Geralt and Keira Metz have to find sign that is associated with Ciri's horse Kelpie left by a masked elven mage. That could prove a bit difficult, since to find it Geralt had to jump in a deep well.