Highlighting Terms in Specific Contexts.
Italics. Key terms in a particular context are often italicized on their first occurrence. Thereafter they are best set in roman.
"Scare quotes." Quotation marks are often used to alert readers that a term is used in a nonstandard, ironic, or other special sense. Nicknamed "scare quotes," they imply, "This is not my term" or "This is not how the term is usually applied." Like any such device, scare quotes lose their force and irritate readers if overused.
In works of philosophy, single quotation marks are sometimes used for similar purposes, but prominent style guides discourage that practice unless it is essential to the author's argument and not confusing to the readers.
"So-called." A word or phrase preceded by so-called should not be enclosed in quotation marks. The expression itself indicates irony or doubt.
Source: The Chicago Manual of Style