Decay refers to the process or state of deterioration, disintegration, decomposition, or decline. It can be used in various contexts such as physical decay where an object loses its structure and strength over time due to natural processes like rusting, rotting, or wearing away; biological decay where living organisms break down dead matter into simpler forms of existence; radioactive decay which is the process by which unstable atoms lose energy by emitting radiation in order to reach a more stable form. In addition, it can also refer to moral or social decay, meaning the gradual decline and corruption of values, customs, institutions, or standards within a society.