This is a spec. Multi-level security is a high-level concept - and not one that has much technical definition - the Wikipedia article (while problematic / vague

This is a spec. Multi-level security is a high-level concept - and not one that has much technical definition - the Wikipedia article (while problematic / vague) even includes some thoughts on semantic overload. As someone who works in security, it's not something that comes up - specific frameworks, applications & implementations are more relevant. Avoiding every possible acronym clash in tech is not particularly viable today (and becomes less so daily). --- Meanwhile, in the context of IETF's work, the acronym is natural and intuitive: Transport/Multiplexed-Transport -vs- Message makes immediate sense to anyone working with security in the context of network protocols.