A spacer is generally something used to create a space between two objects, often to properly position them.

There are also a number of specialised usages for the term.

• Asthma spacers are used to ensure proper delivery of inhaled asthma medication.
• Orthodontic spacer
• Spacers, the first humans to emigrate to space in Isaac Asimov's Robot Series
• in space opera, and science fiction and Role-playing game|roleplaying games in general, the word is often used to refer to humans in general or a specific caste of humans who live in outer space, or (by analogy with "sailor") serve as the crew of spaceships.
• molecular spacers on a molecular level