Threshold, which refers to the part of the floor at the entrance to a room or building, signifies the beginning of something.
This is quite a popular, useful concept in engineering, enables one to make more appropriate decisions regarding health of a system and each of its components, just by observing system performance.
Current threshold: The minimum current level which produces a given effect, result, or response, such as detection, ativation, or operation. For example, the lowest current needed to sustain lasing action in a diode laser.
Sound threshold: The minimum sound pressure level necessary to be detected by human ears.
Frequency threshold: The minimum or maximum frequency which produces a given effect, result, or response, such as detection, activation, or operation. For example, each of the cutoff frequencies of a filter, amplifier, or waveguide.
But this concept is not at all popular in the affairs of life and living, where it could have defined a boundary for all our considerations. As a parameter, threshold could have marked the point beyond which what we consider as a radically different state of affairs exists. Which could have greatly altered our thoughts about everything that leads us to a change in view. And new ideas about good or bad, acceptable or unacceptable, healthy or sick, right or wrong etc. Or, could have helped us in prescribing rules of conduct, more conducive to social tranquility. Easier life and a better world!