What is entropy?

I've mentioned this several times but never really explained it. Entropy is a very important concept in thermodynamics and it has meaning in cosmology. It cannot be ignored. It's what we see everyday but don't really know what's going on. You have to put gas in your car; metal rusts; your house is in need of repair; you get a electric bill every month; your washing machine wears out; you get hungry and have to eat; you can't fall up. All of these are a result of the second law of thermodynamics.
The second law of thermodynamics says that a thermodynamic process will tend to go toward a state of equilibrium and the entropies of whatever comprises the system will increase. The reason this law was made is because no one has been able to make a perpetual motion machine, a machine that would run forever without any energy being fed into it. Even Leonardo Da Vinci realizes that this idea was impossible to achieve, not that it deterred people from tying to do it.
The only way that entropy won't increase is if you are using a reversible process. This is a process that doesn't involve heat transfer from the outside. It's a process that has to be in equilibrium at all times. If these conditions are not met, the process is irreversible and entropy increases. Needless to say, most processes we are familiar with are irreversible. In order for a process to be reversible it would proceed in infinitesimal intervals and take an infinite amount of time. In other words, it's impossible to have a reversible process, at least in this corner of the universe. Just as an addendum, entropy was originally defined as an integral (calculus) of the incremental transfer of heat in a system divided by the absolute temperature. This was essentially an ideal definition that can never be achieved.
Entropy is best defined at a measure of disorder in any system. In other words thermodynamic processes cause a system to become less ordered, which in most cases mean that they fall to a lower energy state. Most processes want to fall to a lower energy state. It's like when you get tired and you want to fall into bed and sleep or at least rest. The only way to recover and keep going is to drink an energy drink. In other words you have to pump energy back into your body to keep going. You can blame that on entropy.
The problem with entropy is that it can't be measured. It has to be calculated. Actually, it's the loss of energy from a process that is forever lost. It's lost to the chaos of the universe and it will continue to be lost as long as the universe exists.
Basically, you can think of entropy as wasted energy. Every machine loses energy in the form of heat in the process of doing work, and it's the reason you must keep feeding motors and engines energy in the form of fuel or electricity. There are lots of other consequences of the inevitable increase in entropy. It's why we experience loss of transmitted energy over power lines; why all motors and engines are not completely efficient; why the sun is gradually heading toward its death; and why we will eventually die. Now you see why it's so important.
Thanks for reading.