I would venture to say that to most (aka the great unwashed) it means little more than beer, barbeque, volleyball and pretty girls in shorts and tank tops. To many, it has some sort of muddled meaning being diffused and blended with the Constitution and other elements of the "founding." Some even associate it with "patriotism" (which they erroneously confuse with "nationalism"), Old Glory, and the uS government.
It is indeed, none of the above. It is supposed to be a "celebration" of the signing of the Declaration of Independence--a revolutionary document like none other in the history of mankind--a document of secession.
I hope you will take the time to read it completely. As you do, please pay particular attention to the listing of the "long train of abuses and usurpations" resulting in "absolute despotism...repeated injuries and usurpations...and the establishment of an absolute tyranny over these states."
As you read, insert "It" (the FedGov) where you see "He" (the King) and substitute the current facts and sorry state of affairs. If you will do that, you will discover that today is no longer a day of "celebration." It is a day of "mourning." And while you read, think secession!