"Mashiach" - the "Messiah," the "Anointed One," the Redeemer of Israel who will appear in history "B'Acharit HaYamim," at the "End of Days," to redeem Israel from its enemies. There are two opinions (naturally!) as to what the nature of the Messianic Period will be.
According to the RAMBAM, there will be no radical change in the way the world works, no change in nature, and the Prophecies which, when taken literally, seem to refer to such changes, such as "And the wolf shall lie down with the lamb" (Yeshayahu 11:6 ) mean that it will be a time of peace, Israel will no longer be under the domination of other nations, the Temple will be rebuilt in Jerusalem, and the study of Torah will reach new heights and depths, "And the world will be filled with the knowledge of Hashem as water covers the bed of the sea", but all with no fundamental change in nature.
According to the RAMBAN, there will be a radical change in nature, and the world will resemble the world that Adam found in "Gan Eden," the "Garden of Eden." The prophecy cited above means that there will be a change as well in the character of "wild" animals, also involving a reversion to the state in which Hashem created the world. And human beings will again have the full potentialities as were possessed by Adam and Chava ("Bereshit"/Genesis 1:23-25 ), before their sin.