In short traditional DNS is only capable of mapping information in text format such as IP addresses.
ENS is a name service system that specifically being built for the blockchain system. Not only can it map the Ethereum addresses but also map decentralized data storages(Swarm) on the blockchain to achieve a truly decentralized data storage with IPFS.
Right now the ENS system is compatible with the DNS system by setting up a mapping to the DNS server. To know more about this technique, please reference to: https://docs.ens.domains/en/latest/dns.html.
Reference
ENS: https://docs.ens.domains/en/latest/
IPFS: http://ipfs.io/
Ethereum Swarm: https://github.com/ethersphere/swarm
