What is the BABYLON that's been sung about in almost every reggae song?

It’s a town on Long Island.

urban dictionary

The term Babylon encompasses the essence of deceptive consumerism that captivates our modern culture and preys upon the pride, ego, and arrogance of those who still suffer from the lies we have all been taught since childhood.

@mcbealer provided a very good link. In respect to reggae, submittal four fits my understanding of its usage:
“Babylon is a word that jamaicans use to compare their experience of being brought to the americas to the jews being brought to babylon during the babylonian captivity. Babylon refers to the place of captivity as well as the power structure that keeps them there. It can also apply to imperial powers and commercial powers such as corporations and governments.”

There is mixing of history in the way the term Babylon is used/sung about in Reggae. Basically it’s an all encompussing term used for that which is “western”, and therby all things colonial, opperessive, capitalist (as in taking unfair monitary advantage of the weak), and dominaring.
It’s used in Reggae music, (a prodominanently Rastafarian expression of music, with it’s originating prophet being Halaiee Salasiee, an Ethopian turn of the century ruler who overthrew the Italian colonial rule) as referring to all things wrong and evil.
When tribes in Africa and Arabia were scattered, Babylon (then a large cosmopolitan city, the center of power, currently in modern day Iraq), was representative of all things modern/evil. In later times Babylon was all things Roman and the hedonistic Rome itself was reffered to as Babylon. In colonial times Babylon became some/all places/things/ways Western.

“By the waters of Babylon…” was a catchphrase in my youth.

In the bible, “Babylon The Great” refers to false religion. Revelation 17, and 18 talk about Babylon the Great being a harlot fornicating with Kings and and 18:23 refers to her making being involved in “spiritistic practices”. So, it is obviously symbolic of an institution which is closely aligned with politics (kings) and engages in ‘spiritistic practices’, which leads to the conclusion that it must be impure religions.