noun
Technical term used in mathematics, logic, or formal contexts to denote a relationship where two entities are equal or equivalent in a specified sense.
数学では、相等性は厳密に定義される。
In mathematics, equality is strictly defined.
同等 means 'equal in rank, value, or quality' and is more common in everyday comparisons, whereas 相等性 is a technical noun for the abstract property of being equal.
Compound of 相等 (sōtō, 'equal, equivalent') + 性 (-sei, '-ness, -ity'), forming an abstract noun meaning 'equality' or 'equivalence'.