Attack Decay Sustain Release (ADSR) is a model used in sound synthesis and music production to describe how a sound evolves over time. It consists of four stages: Attack, which is the initial rise in sound level; Decay, where the sound decreases to a stable level; Sustain, the period where the sound maintains its level; and Release, the final fade-out after the note is released. Each stage plays a crucial role in shaping the character of a sound. For example, a fast Attack can create a sharp sound, while a longer Release can produce a smoother fade. Understanding ADSR helps musicians and producers create more dynamic and expressive audio.