The absolute threshold for hearing is defined as the lowest intensity of a sound that can be detected by an individual at least 50% of the time. While specific measurement criteria may vary, this threshold serves as a practical reference point for understanding auditory perception.

The threshold of hearing refers to the quietest sound that can be detected by the human ear, typically around 0 decibels. The absolute threshold of hearing, on the other hand, is the lowest intensity at which a sound is perceived 50% of the time--it may include factors like frequency and duration.

Absolute threshold is the smallest level of energy required by an external stimulus to be detectable by the human senses, including vision, hearing, taste, smell and touch

If by "softest" you mean "just audible" the term is "absolute threshold of hearing" abbreviated ATH

The faintest sound people can generally hear is around 0 decibels. This is the threshold of hearing, also known as the absolute threshold of hearing, and represents the lowest intensity sound that can be detected by the human ear.