Web, domains and email
IETF
Abbreviation for Internet Engineering Task Force
In short and in plain language
The IETF is an open group from many countries.
It writes technical rules for the internet. Its papers describe, say, the address book for domains. They also cover how mail is sent and how certificates are given out.
Hosting and email providers follow these rules when they set things up.
Definition
The IETF is an open international body that develops technical standards for the internet. Its documents are called RFCs and describe, for example, the Domain Name System, email delivery or the issuing of certificates. Hosting and email providers rely on these standards when setting things up.