A data cloud was a collection of information stored electronically.
In 2013, the Great Intelligence used an organisation run by Miss Kizlet to upload peoples' souls through Wi-Fi into the data cloud in order to feed its form; this was performed by disguised robots called Spoonheads. (TV: The Bells of Saint John)
Missy used a Matrix data slice to store the minds of the recently deceased into a data cloud so that the emotions could be altered and upgraded once their minds were downloaded back into converted Cybermen. (TV: Dark Water, Death in Heaven)