Flows-over a period of time

Income, or output, or profits are concepts that make sense only when a time period is specified. These are called flows because they occur in a period of time. Therefore we need to delineate a time period to get a quantitative measure of these. Since a lot of accounting is done annually in an
economy, many of these are expressed annually like annual profits or production.Flows are defined over a period of time.

Flows are defined with reference to a specific period (length of time ) ;hours,days,weeks,months or years.It has time dimension.National income is flow.It describes and measures flows of goods and services which become available to a country during a year.For instance,income of a person is a flow which is earned during a week or a month or any other period.Other examples are – expenditure,savings,interest,depreciation,exports,imports,change in money supply,lending,borrowing,rent, profit ,etc.because magnitude(size)of all these are measured over a period of time.