What is Income?

Legal Definition
Income is the consumption and savings opportunity gained by an entity within a specified timeframe, which is generally expressed in monetary terms. However, for households and individuals, "income is the sum of all the wages, salaries, profits, interests payments, rents, and other forms of earnings received... in a given period of time."

In the field of public economics, the term may refer to the accumulation of both monetary and non-monetary consumption ability, with the former (monetary) being used as a proxy for total income.
-- Wikipedia
Legal Definition
The gain which proceeds from property, labor, or business; it is applied particularly to individuals; the income of the government is usually called revenue.

2. It has been holden that a devise of the income of land, is in effect the same as a devise of the land itself. 9 Mass. 372; 1 Ashm. 136.
-- Bouviers Law Dictionary
Legal Definition
The return in money from one's business, labor or capital invested; gains, profit or private revenue. Braun's Appeal, 105 Pa. 415; People v. Davenport, 30 Hun (N. Y.) 177; In re Slocum, 169 N. Y. 153, 62 N. E. 130; Waring v. Savannah, 60 Ga. 99. "Income" means that which comes in or is received from any business or investment of capi-ital, without reference to the outgoing expenditures ; while "profits" generally means the gain which is made upon any business or investment when bath receipts and payments are taken into account. "Income," when applied to the affairs of individuals, expresses the same idea that "revenue" does when applied to the affairs of a state or nation. People v. Niagara County, 4 Hill (N. Y.) 20; Bates v. Porter, 74 Cal. 224, 15 Pac. 732. See Income tax.
-- Black's Law Dictionary
Legal Definition
That which comes in to a person as payment for labor, or services rendered in some office, or as gain from lands, the investment of capital, etc. See 148 Wis. 456, Ann. Cas. 1913A, 1147, L. R. A. 1915B, 569, 134 N. W. 673.
-- Ballentine's Law Dictionary