International Dance-Exercise Association
Yes, it originally stood for International Dance Education Association, but now they just go by the association for fitness and wellness professionals.
I would only add 'world's largest' to 'association for health and wellness professionals.'
As I remember when the association was founded personal training was not a force within the fitness community. Wendy and Peter Davis originally set out to create a professional and certifying association for people who taught group exercise, which at that time was generally some form of 'dance' aerobics, growing out of the work of people like Jazzercise founder Judi Missett. That is where the INTERNATIONAL DANCE EXERCISE ASSOCIATION came from. The certifying part split off to form ACE many years ago, and IDEA as it grew enormously also became home to many members of the growing personal training world, and later to quite a few teachers in the mind-body world.