Boat building, one of the oldest branches of engineering, is concerned with constructing the hulls of boats and, for sailboats, the masts, spars and rigging.
Perhaps the most common is the term bucks as a reference for US Dollars. Other common slang terms for dollars include cash, dough, moolah and smackers.. There are various other slang terms for money as well, some of which are general terms and others that are specific to certain denominations of money.
It means to have a lot of money. Typically this is used to describe income gained through the drug trade. Racks are stacks of paper (money). So if you have racks on racks on racks then you have piles of cash. The term was made gained popularity in hip hop culture after the song by YC.