Building - well that's the goal at least, it has to represent something we build.Information - There has to be data behind it, intelligent AEC centric data that understands the general types of objects as well as the flexibility to leverage the minutiae of data that we add for a multitude of purposes.
Model(ing) - It has to be in 3D.
Ok, so for those that say BIM isn't software I will in short agree with you. It is a bunch of software. Revit is BIM unless you use it exactly like CAD (detail lines, detail components, filled regions only) and that is a huge "if". No one does that. Many users don't take advantage of every nook and cranny of Revit but as long as they use walls and doors, that's a BIM. I guess my point is: BIM begins at conception.
There are other tools, I admit, but as far as the de facto BIM Authoring tool? Revit, without equivocation. If you doubt that just look at every BIM guideline out there 10 to 1 is specifies Revit (probably 100 to 1 but I am ballparking it). Now the bunch of software that I allude to is meant to show that there are BIM authoring tools (e.g. Revit, Tekla) and there are BIM leveraging tools (e.g. Navisworks, e-SPECS, Solibri, Virtual Environment, Affinity, SmartBIM). It has to come from somewhere and that is software and then it exists and is taken advantage of in software.
So for those that say "BIM is a process not software" please rethink this. Is Sketchup BIM? No. it might be a building model but it lacks the AEC intelligent information (I guess it’s a BM them, ha ha). So Revit is BIM, ok I feel better now.