IETF
Acronyminternet-engineering-task-force, rfcDefinition
The Internet Engineering Task Force — the open body that standardizes the internet's protocols below the page: HTTP, TLS, DNS, URLs and URIs, JSON, OAuth, WebSockets — as numbered RFCs, by rough consensus and running code
No membership; anyone on the mailing list is a participant. An RFC (Request for Comments) is the publication format, and some are standards while others are informational, so the number alone says nothing about status. When a web page names an RFC — 9110 for HTTP semantics, 3339 for the date format in an Atom feed, 8259 for JSON — this is where it lives.
The layer under the W3C's. The consortium says what a page is; the task force says how it gets to you. A browser implements both, which is why a front-end engineer meets both.