Half-Life
A probabilistic rate of decay where the quantity of something is reduced by half. Used most often in physics to describe the exponential decay of radioactive elements.
Origin
New Zealand-born physicist Ernest Rutherford coined the term "half-life period" in 1907 while working at McGill University in Montreal. The term was shortened to simply "half-life" in the early 1950s. Rutherford received the 1908 Nobel Prize in Chemistry for his investigations into the disintegration of elements.
Everyday Use
We experience "decay" in our everyday lives, whether in habits that have gone stale, knowledge that we acquired through formal education but now struggle to recall, or skills that dwindled without practice. Reminding ourselves that all of these things have their own "half-life" helps us to not take it personally — that often our assets exhibit a 'use-it-or-lose-it' quality that must be cultivated and grown.