Why are noble gases also called inert gases?

Noble gases are referred to as inert gases because they are chemically unreactive, or nearly so, under standard conditions. This lack of reactivity stems from their stable electronic structure; their atoms hold their full quota of electrons strongly, possess no affinity for additional electrons, and show little tendency to share electrons with other atoms.12

Because of this indifference toward other substances, noble gases are frequently used to provide protective, nonreactive environments for industrial processes such as welding, refining metals, and electronics manufacturing.3

It is important to note that the term "inert" is a generalization. While noble gases were historically considered completely unreactive, it is now known that some, such as krypton, xenon, and radon, can form stable compounds under specific conditions. Furthermore, the synthetic element oganesson is predicted to be more reactive than its lighter counterparts, potentially breaking the trend of inertness entirely due to relativistic effects associated with its large atomic size and mass.3