The scientific term used in radioactivity and it states that, 'How much time a quantity will take to decrease to it half of the original value'. The theory was formulated after the Ernest Rutherford experiment in the beginning of 20th century. Half-life is used to describe the time of decay for a quantity from its origin to the time it will take that value to reduce to the half.
Diagrams
Originated from/Coined by
Ernest Rutherford
Further Reading/ References
https://en.wikipedia.org/wiki/Half-life