Hermetically sealed is used in vacuum environment

Hermetically sealed is used in vacuum environments i.e. space applications.  I've applied the technology on a Ion Beam Implant Chambers or a Linear Accellerator's Low Energy and High Energy Beam Transports.  I've worked as Mechanical Engineer  on both types of systems over the years. A hermetically sealed weldment or similar is air tight and vacuum leak tested as measurement in Torr Liter/Second.