While there's still no details on what Mirror's Edge: Catalyst actually is (other than a recently-filed trademark and website domain), the official Mirror's Edge Twitter account has tweeted a picture of the dictionary definition of the word - or at least a definition of it - in what appears to be a tease for fans.
#mirrorsedge pic.twitter.com/hTG9sZRbARJune 8, 2015
The definition reads, "a person or thing that precipitates an event. 'she acted as a catalyst for change.'" Said tweet also features the word "catalyst" in a fancy font, and the hashtag "mirrorsedge."
This all seems pretty applicable to Mirror's Edge heroine Faith, who certainly sought to change her world by becoming a Runner. The mystery continues.