Opamp input offset voltage...common mode?
The circled expression is under the "Test Conditions" heading so it is describing the conditions under which the input offset voltage was measured.

V+ is the name of the positive power supply pin:



The non-inverting and inverting inputs are called +IN A/B and -IN A/B, respectively.

The expression is therefore telling you that the input offset voltage was measured with a common mode voltage set to 1.5V below the V+ voltage. This information is necessary because the top of the table (which you can see in your screenshot) says that


  \$V_{\text{CM}} = V_{\text{OUT}} = V_{\text{S}} / 2\$ ... (unless otherwise noted)


Without this note you would assume the common mode voltage was \$V_{\text{S}} / 2\$ when the input offset voltage was measured. That measurement is given in the first three lines of the input offset voltage specification (where each of those lines is for different temperatures).