it means a whole lot better than 300 dpi, like what we used to have.
2,880 x 720 is the resolution across the paper feed, while 720 is the resolution along the paper feed (or is vice versa?) I haven't a clue what optimised means, but I guess it is much the same hype as RET = resolution enhancement technology.
Resolution is so high nowadays that there seems little to choose between modern printers here. Better take a look at some actual printouts to see what the quality is really like. The numbers have become meaningless.