Immediate early genes (IEGs) are a group of genes that are rapidly activated in neurons and other cells following various external or internal stimuli. These genes play important roles in neural development and plasticity, learning and memory, and neuronal activity regulation. There are several synonyms for immediate early genes, such as immediate response genes, primary response genes, and rapidly induced genes. The term "immediate" refers to the fact that these genes are immediately activated upon exposure to a specific stimulus, while "early" implies that their expression occurs early in the cellular response cascade. Understanding the molecular mechanisms underlying IEG activation could lead to the development of novel therapeutic strategies for a range of neurological disorders.