x_{1 }= t_{1} is the elapsed time required for decaying/diminishing/reducing/shrinking population x_{2 }= g_{1} to decrease in number by a factor of exactly/approximately half according to standard/under condition/by model/in experiment x_{3}; x_{1} is the half-life of population/sample x_{2}; the (approximate) halving of population x_{2} takes approximately x_{1} (dimensionful number: time).

Many of the veljvo terbri can be derived from those which are present. This word may refer to a duration that is statistical (for large samples, the average time required for half of the population to probably disappear/become invalid), ideal (guaranteed rather than statistical), or experimental (in a given trial, some number was recorded on a stopwatch when the count decreased by half). See also: gritezdybi'otei, grixonbybi'otei.

- gritezdybi'otei
- x
_{1 }= t_{1}is the elapsed time required for decaying/diminishing/reducing/shrinking population x_{2 }= g_{1}to decrease in number by a factor of exactly/approximately 1/e^(x_{3)}from that which is considered to be the initial population size, where e is the natural exponential base and x_{3}[li; default: 1] is a real number, according to standard/under condition/by model/in experiment x_{4}; x_{1}is the one-(e^(x_{3))}-th-life of population/sample x_{2}; the (approximate) (x_{3)}-th one-e-th-ing/e-fold decrease(/increase) of population x_{2}takes approximately x_{1}(time). - grixonbybi'otei
- x
_{1 }= t_{1}is the elapsed time required for decaying/diminishing/reducing/shrinking population x_{2 }= g_{1}to decrease in number by a factor of exactly/approximately 1/(x_{3)}from that which is considered to be the initial population size, where x_{3}[li; default: 1] is a positive real number, according to standard/under condition/by model/in experiment x_{4}; x_{1}is the (x_{3^(-1))}-th-life of population/sample x_{2}; the (approximate) one-x_{3}-th-ing/(x_{3)}-fold decrease(/increase) of population x_{2}takes approximately x_{1}(time).