On 31 Mar 2013 HTG provided a definition of Ad Hoc Networks (AHNs) based upon what the author understood at hoc to mean. Then he used the example of a network set up on the fly for a specific reason, such as "an Ethernet cross-over cable to transfer files between two computers". This is NOT what AHNs are. His description at the start of the discussion is closer to what an AHN is when he said "refers to the the non-dependence of the ad hoc network on pre-existing infrastructure. Wikipedia gets it right when they say "the determination of which nodes forward data is made dynamically on the basis of network connectivity. In addition to the classic routing, ad hoc networks can use flooding for forwarding the data."
The company i worked for provided ad hoc networks for the military. The goal was for a network that was smart in that it organized its own routing on the fly. New nodes could join the network and the routing tables would be updated. Part of the goal was flexibility but also survivability: one node could be disabled and the network would "heal" itself and reconstruct routing tables to ensure that the traffic was delivered.
But an AHN certainly is not a network or communication interconnect that is put up at the spur of the moment for something like used in the examples.