What is the meaning of Fe in Fe415 grade reinforcement steel?

The abbreviation Fe stands for Ferrous material ie iron from which the reinforcement steel bars are manufactured.

The reinforcement steel bars used in RCC (Reinforced Cement Concrete) are designated in grades of Fe250, Fe415 or Fe500 depending on their Yield Strength.(The numbers 215, 415 and 500 tell about this Yield Strength in N/mm2 the bars are designed and manufactured to have.)

Fe415 indicates that the Yield Strength (tensile strength when it is subjected to elongation) of steel is 415 N/mm2.