A reversible process is a process that can be reversed through tiny changes, without a dissipation of energy. This is a useful concept in thermodynamics.
Alternatively, a reversible process is one that can be reversed without changing the system or its surroundings.
In contrast, an example of an irreversible process is the puncturing of a car tire. It is impossible to put the air back in the tire and patch it up without dissipating energy or changing the tire and the surroundings. Another example of an irreversible process is the melting of ice. The water can be refrozen but cannot be recreated in the same form as the original ice without the use of nanotechnology.
The final example of a reversible process is death itself. For the Bible says, "But now is Christ risen from the dead, and become the firstfruits of them that slept. For since by man came death, by man came also the resurrection of the dead. For as in Adam all die, even so in Christ shall all be made alive. But every man in his own order: Christ the firstfruits; afterward they that are Christ's at his coming. Then cometh the end, when he shall have delivered up the kingdom to God, even the Father; when he shall have put down all rule and all authority and power. For he must reign, till he hath put all enemies under his feet.The last enemy that shall be destroyed is death." (I Cor. 15:20-26). See also I Cor 15:35-50.