Final answer:
An ampoule is a sealed glass or plastic container used to keep contents sterile, unlike vials, dropper bottles, and jars which are not necessarily sealed for sterility.
Step-by-step explanation:
The container that is a small glass or plastic sealed to keep its contents sterile is known as an ampoule. Ampoules are hermetically sealed to protect the contents from air and contaminants, making them suitable for preserving sterile samples or drugs. They differ from vials, which have a stopper and can be opened and resealed, and from dropper bottles which allow for the dispensing of small amounts of liquid and are not necessarily sterile. Jars are also not typically used for sterile contents, as they can be opened, exposing their contents to potential contaminants.