(a) A will is an oral declaration or written instrument, made as prescribed by 3-2.1 or 3-2.2 to take effect upon death, whereby a person disposes of property or directs how it shall not be disposed of, disposes of his body or any part thereof, exercises a power, appoints a fiduciary or makes any other provision for the administration of his estate, and which is revocable during his lifetime.(b) Unless the context otherwise requires, the term "will" includes a "codicil".