NS records, or nameserver records, define which authoritative nameservers contain the DNS records for a domain.
You can use NS records to delegate DNS queries between multiple DNS providers for a domain or subdomain. For example, if you purchase a domain through GoDaddy.com but want to manage your domain’s DNS records using DigitalOcean, you need to edit the NS records for your domain at GoDaddy.com to indicate that DigitalOcean’s nameservers are the authoritative servers for your domain’s records.