What did the Ashok chakra on the flag of India originally represent?

The Ashoka Chakra on the flag of India is a depiction of a 24-spoked Dharmachakra (Wheel of Dharma, or Wheel of Life) -- originally a Buddhist symbol but now standing for all the religions of India.

It replaced the charkha (specifically, a spinning-wheel, and a symbol of the Indian independence movement) which had featured on pre-independence versions of the flag.