A condescending buzz word used when someone disagrees with someone else's solution to a problem, and by using this word they call into question the method used to solve the problem instead of offering any truly useful input. This term is quite often used in situations where someone is trying to stop someone else from being productive.
Person 1: "I've just about had it with Bob's solutioneering. He always pitches answers to problems without defining the problem."
Person 2: "Well, do you have any better ideas on how to solve the problem?"
Person 1: "ummmmm...."