What does criticality mean?
Criticality refers to the quality of being critical — that is, of being decisive, essential, or poised at a turning point. Its most precise and prominent use is in nuclear physics, where it describes the exact state in which a fissile substance sustains a self-perpetuating chain reaction: when a reactor 'reaches criticality,' it has achieved a stable, controlled reaction, not a runaway one. The word also appears in mathematics and physics to describe systems at a critical point where behavior changes abruptly, and in management and engineering to rank how vital a component or task is. Though it sounds dramatic, especially in phrases like 'going critical,' criticality is a neutral technical term. Derived from the Greek kritikos via Latin and French, it belongs to the same family as critic and crisis, all rooted in the idea of judgment and decision.
nounThe quality, state, or degree of being critical; in technical contexts, the condition in which a system — such as a nuclear reactor — reaches the exact point at which a self-sustaining chain reaction or process becomes possible.
- In nuclear physics: the state in which a fissile system sustains a self-perpetuating chain reaction at a steady rate.
- More generally: the quality of being crucial, decisive, or of decisive importance.
- In mathematics and physics broadly: a point at which a system's behavior changes qualitatively (a critical point).
"Engineers carefully monitored the reactor as it approached criticality."
"The reactor achieved criticality for the first time on Tuesday, marking the start of commercial operation."
"Given the criticality of the deadline, the team worked through the weekend."
Rarely used in practice; the plural may appear in technical literature referring to multiple distinct critical states or rated levels of importance.
"The safety review assessed the criticalities of several subsystems."
In nuclear engineering, 'going critical' sounds alarming — but it's actually the normal, carefully controlled moment a reactor starts producing power.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of criticality
Criticality derives from 'critical,' which traces back through French critique to Latin criticus and ultimately Greek kritikos, meaning 'able to discern or judge,' from krinein, 'to separate or decide.' The suffix '-ity' forms abstract nouns denoting a state or quality, so criticality literally means 'the state of being critical.' It was adopted into scientific English in the nineteenth century as physics developed the concept of critical states, and became central vocabulary with the rise of nuclear science in the twentieth century.
Related word forms
How criticality is actually used
In everyday language, 'criticality' is relatively rare — people more often say 'critically important' or simply 'crucial.' It appears most frequently in nuclear engineering, risk assessment, and project management contexts. In nuclear settings it carries no negative connotation despite its dramatic sound; 'subcritical,' 'critical,' and 'supercritical' are neutral technical terms describing reaction rates.
Easily confused with criticality
Criticality is the state of sustaining a chain reaction, while critical mass is the minimum amount of fissile material needed to reach that state.