What does DNS resolver mean?
A DNS resolver handles a client's name-resolution requests, obtaining or returning the relevant answer. Many home devices use the resolver supplied through network configuration, while some applications implement their own behaviour. Browser settings may not control every television app.
Why it matters
A resolver is another service to evaluate for reliability, privacy and filtering. Use published setup information rather than an unexplained address from a forum. If you test a replacement, change one device first where supported and retain a route back to automatic configuration. A different result does not by itself prove that the previous provider deliberately blocked media.
A practical example
A browser using encrypted DNS can load a site while another application uses the operating system's resolver and fails. That difference concerns configuration scope, not proof that both applications followed the same request path.
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Related terminology: DNS over TLS, DNS time to live.
For practical setup and troubleshooting, browse the journal or support guides.