The definition I'm aware of is being hacked together (rapidly and cheaply) and flimsy, as opposed to engineered and robust.

Not to be confused with something that is "engineered" (as in, plenty of resources are dedicated to it) yet still flimsy, like so much of the software we know.

In certain circumstances it means an inelegant but effective and cheap workaround, so basically one of the sub-meanings of "hack"

Being inexpensive and fast apparently..