Pre-tax income is operating-income plus or minus everything non-operating: interest-expense, interest-income, other-income-and-expense and results from equity-method-investment stakes.
It is useful as a comparison point because tax rates jump around with one-off settlements and geography, so pre-tax profit can grow smoothly while net-income does not.
Example: Northwind Tools has operating income of $120M, interest expense of $18M and interest income of $30M, giving pre-tax income of $132M. At a 25% effective-tax-rate, net income is $99M.
Related: operating-income, income-tax-expense, effective-tax-rate, net-income, other-income-and-expense