domain name system – RFC 8767 and delegation

I do not get the following sentence from the RFC 8767:

When no authorities are able to be reached during a resolution
attempt, the resolver should attempt to refresh the delegation and
restart the iterative lookup process with the remaining time on the
query resolution timer. This resumption should be done only once per
resolution effort.

Specifically:

the resolver should attempt to refresh the delegation

What do we call delegation here? I do not understand why it is talking about delegation when it comes to recursive resolver.