LiPo or NiMh

5s stands for the number of cells wired up in series. each li-po cell has a nominal voltage of 3.7V, hence 5 cells in series is 5 x 3.7 which is 18.5v.
the 20c stands for the discharge rate that the pack can handle continously. 1C is equal to the capacity of the battery, hence in your case 1C is 2300mAh.
that means the battery can handle a continuous discharge rate of 20 x 2300mA = 46000mA or 46 Amps of load.