[sfteus]

Been a while since I've done anything related to audio engineering so my terminology might not be correct, but I've always heard this described as presence. Stems from old guitar amps that had presence knobs that would dump highs to ground to give a darker, slightly muffled sound.

Like you said, it's the difference between it sounding like you're in a small room with a band or in a large venue where some of the clarity is lost.