The definition used on the material once hosted on GW's homepage seems pretty simple. "Sentient machinery" and "machines that can think fully for themselves", which to me is exactly what an Artificial Intelligence is all about.
To me it would seem that "Abominable Intelligence" is just a 40k'ified term for "Artificial Intelligence". They both use the same abbreviation and mean the same thing; the full name simply morphed into its current term following countless years of decline in technological knowledge and propagation of the belief that AIs are an evil thing. Just like the Men of Iron occasionally mentioned in Imperial history are obviously not actual men of iron but simply robots (with an A.I.) with a fancy name bestowed by people who don't understand them anymore.
It's part of the Grimdark theme, and I am relatively sure there are more examples for such "falsified" terms to be found in the setting. Take the "Hellgun" for example, which just used to be called HEL-gun (for High Energy Laser). Or the RH-1N0, which is "now" called a Rhino. Nobody in the Imperium remembers the actual names these things were once called, and with "Abominable Intelligences" it's the same.
But I guess our perceptions of the topic are just different. For the record, I also think that a Titan would use a similar means to compute its information than a Land Raider.
No big deal, though. When you follow your own interpretation for this, it does line up and make sense, so it's all good.
current 40k RPG character: Captain Elias, Celestial Lions Tactical Marine