From third grade, the "X" means multiply! This is a 2760 revolutions per volt motor.
For LiPo batteries, the "X" is the number of cells in the battery. For the LiPo, "X3" is three cells; i.e, a 3S LiPo battery.
For the props, the "X" is the number of blades. The "5040X4" would be a five inch, four blade prop. The 4045X3,5040X3,5045X3 are three blade four inch, and five inch props. The "5045" in the last row is a two blade prop which does not need a multiplier designation. For obvious reasons, there are no one blade props; like left handed screwdrivers!
Hope this helps!