大般涅槃經集解 52.52

52.52

案僧亮曰：非無不偏，故名中也。雖復中名是同，中義異故，言不定也。

Sengliang states: Being neither non-existent nor biased, it is therefore called 'middle'. Although the name 'middle' is the same, the meanings of 'middle' differ, hence he says 'not definitive'.