Robin Hanson defines it:
“Tolerance” is a feel-good buzzword in our society, but I fear people have forgotten what it means. Many folks are proud of their “tolerance” for gays, working women, Tibetan monks in cute orange outfits, or blacks sitting at the front of the bus. But what they really mean is that they consider such things to be completely appropriate parts of their society, and are not bothered by them in the slightest. That, however, isn’t “tolerance.”
“Tolerance” is where you tolerate things that actually bother you. Things that make you go “ick”, or that conflict with strong intuitions on proper behavior. Once upon a time, the idea of gay sex made most folks quite uncomfortable, and yet many of those folks still advocated tolerance for gay sex. Their argument was not that gay sex isn’t icky, but that a broad society should be reluctant to ban apparently victimless activities merely because many find them icky.
Alex Tabarrok moves the football a few more yards down the field.