A change in an organism's environment that can cause a response is termed a stimulus. Stimuli can come in various forms, such as changes in temperature, light, moisture, or the presence of predators. Organisms respond to stimuli through various physiological or behavioral adaptations, enabling them to survive and thrive in their environments. This response can be immediate or involve complex biological processes. Understanding how organisms perceive and react to stimuli is vital in the fields of biology, ecology, and psychology.