Activated

Activated is the past participle of activate and an adjective used to describe something made active, operative, or ready to function. The term appears in science, engineering, medicine, and everyday language to indicate that a process has begun, a device is switched on, or a substance has been prepared for use.

In chemistry and materials science, activation refers to the initiation or enhancement of a process. Activation energy is the minimum energy required for a reaction to proceed; an activated complex (transition state) represents a fleeting arrangement of atoms at the top of the reaction barrier. Materials labeled activated, such as activated carbon and activated alumina, have undergone processing to increase surface area and adsorption capacity, useful in filtration, drying, and catalysis. Activation can also denote making a molecule more reactive, for example by functionalizing a substrate or using catalysts to activate bonds.

In biology and medicine, activation describes stimulation that enables a system to respond. Immune cells, notably T cells, become activated upon encountering antigens, leading to clonal expansion and effector action. Enzymes can be activated or deactivated by cofactors, phosphorylation, or proteolysis, thereby controlling metabolic pathways. In neuroscience, neurons are said to be activated when they fire an action potential. Clinically, activated charcoal is used to adsorb certain poisons, and activated sludge is a microbial process used in wastewater treatment.

In technology and everyday use, activation often refers to enabling functionality. Software and devices may require activation through license keys or online verification before full use. In machine learning, neurons or units are activated by an activation function, which shapes their response to input. The term also appears in contexts describing preparedness or readiness, indicating that a system or component has been enabled and is ready to operate.