What is a threshold in terms of biology?

What does it mean by absolute threshold and difference threshold?

The threshold in biology is explained in terms of neuroscience or action potential that affects nervous system.

The threshold value is the value that identifies incoming signals that should be sufficient enough to generate an action potential. The potentials generated by the signals are additive, and reaches threshold depends on their amplitude and frequency.

An absolute threshold is defined as the minimum level of signals like light, touch or sound, detected by any organism and allows them to react.

While Difference threshold allow to detect difference between two different signals.