A hermetic seal is any type of sealing that makes a given object airtight (preventing the passage of air, oxygen, or other gases). The term originally applied to airtight glass containers but, as technology advanced, it applied to a larger category of materials, including metals, rubber, and plastics. Hermetic seals are essential to the correct and safe functionality of many electronic and healthcare products. Used technically, it is stated in conjunction with a specific test method and conditions of use. Colloquially, the exact requirements of such a seal varies with the application.