The "gun show loophole" is an imprecise term, I'll give you that.
But the FACT that people can purchase a gun through various "legal" means without a background is undeniable.
By legal, I just mean that the seller is criminally liable no matter what the buyer does with the gun. Obviously, a felon purchasing a gun is committing a crime… but the seller is not .
What about bad apple gun dealers -- stores that are know to regularly sell guns out the back door to straw purchasers. Tiahrt Amendments limit ATF and state police ability to investigate and monitor this practice. (among others)
Facts to backup my statements -
PolitiFact Sheet: 3 things to know about the 'gun show loophole'