This is situated at the crown of the head. When Kundalini reaches this chakra, the Yogi attains Super-Conscious State. 

The word Sahasrara denotes that this chakra has 1,000 petals, i.e. 1,000 Yoga Nadis originate from this center. As in the case of other chakras, the vibrations made by the Yoga Nadis are represented by the Sanskrit alphabets. All the 50 alphabets of the Sanskrit language are repeated here, again and again, on all the Nadis. 

This is a Sukshma (subtle) center. The corresponding center in the physical body is in the brain. All the chakras have their intimate connection with this center. Hence this is not included as one among the Shat-Chakras