According to our colleagues at Trailhead the Clinton campaign has questioned whether Obama lied when he claimed to be a law professor at U of Chicago. Formally his position was Senior Lecturer. In a way this is almost too silly to merit a response: when you’re taking aclass from someone employed by a university you almost certainly call that person "Professor." Q. E. D. But it is true that law schools make scores of fine distinctions between faculty members, in part because university rules reserve certain titles for people who have passed faculty committees that evaluate scholarly merit. So technically, the Clinton folks are right— "Senior Lecturer" is not synonymous with "Professor," and inside the ivory tower people care a lot about such titles, just as in the ancien regimes of Europe a Viscount who claimed to a Count was a fraud; a Baronet who passed himself off as a Baron would have been taken to task by those with a legitimate claim to that status.
During my twelve years at Stanford (first as an Assistant, then an Associate, then a Full and now a Chaired Professor of Law if you care about such things) many Adjunct Faculty, Visiting Lecturers, Senior Lecturers, Teaching Fellows and Scholars-in-Residence have referred to themselves as "Professors" when dealing with the media and the general public and no one, to my knowledge, has thought that honor or honesty required us to correct the technical misimpression.