Entropy, as basically described, is the idea that the energy that it takes to make something is greater than it takes for something to "break."
Essentially, the energy that goes into creating a cup, is less than the energy to break a cup. This is somewhat flawed, as it's more that the energy is "lost" due to dissipation, but the energy to "capture" that dissipated energy adds onto the "cost" and as long as the "cost" is higher than the return (in other words, as long as it isn't a real perpetual motion machine, or more efficient, that is "entropy.")
Really, the idea is based around energy being Finite (limited) and space being... well... not. In theory, eventually there wouldn't be enough energy in any given area of space for anything to happen with that energy (as talked about in the above linked Heat Death scenario).
Of course, the theory is based on assumptions of how energy behaves, that space is truly endless, energy truly finite (or a "lower infinity" than space), etc.
Considering that AC found an "answer" to the question though... take that for what you will.
Also, it's only one of many theoretical fates, there's also "Big Crunch" (basically, a reverse of "Big Bang" optionally with multiple Crunches and Bangs as a natural phenomenon) and other possible fates... all without getting into the murky domain of quantum physics (where "observation" changes/determines "nature").