Questions related to the earning of money (or other capital) within a specified time frame. Topics such as methods to increase income, account for it, track it, analyze it, or disclose it are all appropriate, but discussions of income tax should use that tag instead.
Income is the consumption and savings opportunity gained by an entity within a specified time frame, which is generally expressed in monetary terms.
Source: Wikipedia
Note: The entity may be a person, family, corporation, or country as these can be taken from various perspectives. In the first couple of cases this is generally about salary, savings and investments that provide the resources for a person or family to live. On the corporate side, income is part of the accounting that is done.