20 CFR § 404.1572 - What we mean by substantial gainful activity.
Substantial gainful activity is work activity that is both substantial and gainful:
(a)Substantial work activity.Substantial work activity is work activity that involves doing significant physical or mental activities. Your work may be substantial even if it is done on a part-time basis or if you do less, get paid less, or have less responsibility than when you worked before.
(b)Gainful work activity.Gainful work activity is work activity that you do for pay or profit. Work activity is gainful if it is the kind of work usually done for pay or profit, whether or not a profit is realized.
(c)Some other activities. Generally, we do not consider activities like taking care of yourself, household tasks, hobbies, therapy, school attendance, club activities, or social programs to be substantial gainful activity.