What is name of the term that describes the time that it takes for 50% of a radioisotope to decay?

Half-life is the term that describes the time that it takes for 50% of a radioisotope to decay. The opposite of half-life is doubling time. Half-life is a constant value over the lifetime of a decaying quantity exponentially. It is not only used in radioactive decay, it is also used in how long unstable atoms will decay or how long stable atoms survive.