Streaming platforms normalise audio to roughly −14 LUFS. Zoomr's loudness normalisation measures your whole mix and brings it to −14 LUFS with a −1 dBFS limiter.
Glossary
What is LUFS (loudness units)?
LUFS (Loudness Units relative to Full Scale) measures how loud audio *sounds*, not just its peaks. It's defined by ITU-R BS.1770.