# time constant

> English word · Noun

## Definitions
1. A characteristic of an exponential function, represented by τ in the function
2. The time in which a physical system's response to a step-wise change in an external variable reaches approximately 63% of its final (asymptotic) value.
3. For radioactivity: the decay constant.

## Source
Compiled from Wiktionary via kaikki.org (CC BY-SA). Data vintage: 2026-05-06.
Canonical page: https://plainspell.com/en/word/time-constant