To most people, the word loophole has a negative connotation. It implies that someone has found a way around something.
When Democrats talk about the gun show loophole, corporate tax loopholes, or the loophole that allows the automatic approval of a gun sale if the FBI fails to provide a background check within 3 days, they are actually talking about laws, passed by Congress and signed by various Presidents, allowing certain things to happen.
Take the so-called gun show loophole referred to by Democrats. This is actually the legal right of a private party to transfer a gun to another private party by sale, gift, inheritance, or loan without the receiving party having to go through a background check. This is how the law is written. And, it doesn't matter if the "transfer" takes place at a gun show, in someone's home, or out of the back of a car. Now, understand, the law also has some serious caveats in the transfer of a firearm that could cause the original owner to be charged with a felony. Those caveats are simply that you can't transfer a gun to another party if you know that party couldn't, themselves, pass a background check, or you are aware that the gun will be used in the commission of a crime.
Then, there are the corporate tax loopholes that both Barack Obama and Bernie Sanders like to talk about. Again, these aren't loopholes. These are tax breaks given by Congress to corporations as incentives. For example, incentives to find more domestic oil and reduce our dependence on foreign oil. Or, to write off the cost of making corporate owned buildings more energy efficient. Or, the accelerated depreciation of certain capital expenses. Believe me, if a corporation does skirt the law, the Internal Revenue Service will be all over it and would advise Congress to ange the law.
Now, Democrat Representative James Clyburn wants to close what he defines as another gun-sale related loophole. This newly minted loophole is the "default proceed rule" under the Brady Bill that allows a gun sale to proceed if the FBI doesn't provide a result to the background check within 3 days. If it was up to Clyburn, you could die waiting for an FBI background check to be completed.
The fact is that Democrats are using the word "loophole" as a disingenuous means to force legislation that would reverse laws that they don't like. That's why every time they want to close such "loopholes" they can get legislation passed because closing them would result in broader consequences.
Definition of Loophole: http://dictionary.reference.com/browse/loophole
The Facts about Gun Shows: http://www.cato.org/publications/commentary/facts-about-gun-shows
Eliminate all oil and gas tax loopholes - PolitiFact: http://www.politifact.com/truth-o-meter/promises/obameter/promise/2/eliminate-all-oil-and-gas-tax-loopholes/
Congressman introduces bill to close loophole that allowed alleged Charleston shooter to buy gun: http://www.businessinsider.com/charleston-shooting-gun-control-bill-2015-7