variability; mutability
Abstract noun describing the quality of being changeable or mutable; used in technical, scientific, or formal contexts.
Because this system has high variability, it can handle various situations.
Genetic variability is one of the driving forces of evolution.
不変性 means 'invariability' or 'immutability', the opposite of 可変性.
Compound of 可変 (kahen, 'variable') + 性 (-sei, '-ity, -ness'). The exact historical derivation is uncertain, but the kanji 可変 is a Sino-Japanese word meaning 'changeable'.