Definition of «to form a seal»

The phrase "to form a seal" means to create a tightly closed or covered space, preventing anything from getting in or out.

A baby with a neurological issue may have difficulty forming a seal around the breast or sucking. (verywellfamily.com)
Ask your child to keep the thermometer in place by forming a seal with their lips. (aboutkidshealth.ca)
Fold up sides of foil to form a sealed pouch. (gourmetdaytoday.com)
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