Degassing

Degassing is the process to release the water and air contained in a molding material, the gas generated during molding, and the air existing in the mold before molding.
Molding large or thick parts without degassing may cause swelling or bubbles on the surface, aggravating the appearance.
Degassing is usually done by making a ditch on the mold or using a hole on the ejector pin.
In the figure below, the land is used to do degassing and air venting.