Q. What is the Definition of Disability for 72(t)?? 

A. The definition of disability can be found in IRC Section 72(m)(7). In one case, Dwyer v. Comm., 106 TC No. 18 (1996), the Tax Court agreed with the IRS and stated… 
For purposes of this rule, an individual is considered disabled if “he is unable to engage in any substantial gainful activity by reason of any medically determinable physical or mental impairment which can be expected to result in death or to be of long-continued and infinite duration.”

The Code specifies that an individual must be able to furnish proof of his disability in whatever form and manner that the Service may require. The court noted that the regulations under Section 72 also state that an impairment that is remediable does not constitute a disability.