URLs in the strict sense are a subset of URIs. They specify a mechanism (like HTTP or FTP) for how to access the referenced resource. The other type of URIs are opaque IDs, like doi:10.1000/182 or urn:isbn:9780141036144. These technically can’t expire, though that doesn’t mean you’ll be able to access what they reference.

However, “URL” in the broader sense is used as an umbrella term for URIs and IRIs (internationalized resource identifiers), in particular by WHATWG.

In practice, what matters is the specific URI scheme (“http”, “doi”, etc.).