Operating income is the profit/loss from ordinary operations of the company without:
It's usually EBIT less the income from investments (e.g. dividends). But if the company´s core business is related to investment activity, these incomes can form part of Operating income.
Operating income is defined by SEC (US Securities and Exchange Commission), its definition, therefore, has the exact wording. SEC also mentions that Operating income is not directly comparable to EBIT or EBITDA. (19) Therefore, above mentioned comparison with EBIT should be considered only as indicative.
However, in practice, it is unfortunately common that the terms EBIT/PBIT and Operating income are used interchangeably or are considered synonymous.