DNSSEC is a protocol that allows a domain owner to cryptographically sign the information in the zone so that a client can be sure that the information retrieved from the DNS servers has not been altered while in transit on the internet. This makes it virtually impossible for anyone else to alter the information in a domain like changing the IP address for www.bank.com to a different IP address than the owner of the domain bank.com have set www.bank.com to point to.
If data is altered by someone else, the signature will no longer match, and the DNS query will fail as long as the DNS resolver verifies the DNSSEC signature.