It originally was only about technology and design but evolved and is now open to any topic. The conferences also branched and you now have some TED conf in India and Paris, and pretty much anywhere where people are interested and can put a great conference together, you could organize it. Then all the content is available online.
Some conferences I really liked:
Evgeny Morozov: How the Net aids dictatorships
From software exec to electric car revolutionary: Exclusive interview with Shai Agassi
Rebecca Saxe: How we read each other's minds I highly recommend this one. It's a wonderful insight on how and why we judge and react to other peoples actions.