A general sort of synonym for "rich," similar in use to "well-to-do." It's often a term used by those who are accused of being rich, but don't much like the snobbery inherently implied with that term. In such a scenario, it's more supposed to mean something along the lines of, "having enough money that I don't need to worry about my accounts, but not having so much money that I can buy solid gold houses and carved diamond wristwatches every other Tuesday."
"I'm not really rich," said William as he paid for everyone's movie tickets, "I'm just well-off."
by Fat People In Leather March 27, 2005