It is a glass-like impenetrable layer formed by exposing a mixture of melted colorants and various materials to high temperatures. The mixture is used for decoration and waterproofing on ceramic products.
Glazes are often described by the temperature at which they melt to produce the results desired by the potter. Glazes can be applied to either unfired ceramics or to already fired ceramics.
Although high heat glazes are durable they are less colorful (mostly due to impurities) compared to low glazes that are more colorful but less durable. It is always advisable and pertinent to consider the type of glaze in terms of food safety, durability, and glaze fit with the underlying claybody.