Abominable Intelligence (A.I. for short) is a term used by the Adeptus Mechanicus for an adaptive, self-enhancing, factitious intelligence with its own consciousness.
During the Dark Age of Technology, these intelligences rebelled against their human masters, leading to bloody wars. Since that time, and by a personal decree of the Emperor himself, it has been forbidden to fabricate or service those machines that are able to think and act independently.
A.I. is not to be mistaken for the machine spirit that has parallels but basal differences - namely, no ability to enhance itself.