Operating income relates to that part of the revenue which is associated with the operating activities of the company. The operating activities are the core business functions which is linked to the sale of goods or services.
For example, XYZ company sells goods online to customers all over the world and this forms the core business activity. The income earned from such activity translates to operating income whereas other incomes will be ignored (revenue from sale of empty cardboard boxes, revenue from bonds etc.).
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