An injection is the act of forcing a liquid (often medicine) into the body using a needle and syringe. When you get a vaccine or certain medications, a nurse or doctor uses an injection to deliver the medicine directly into your muscle or bloodstream, where it can work quickly and effectively.

While shots can feel uncomfortable for a moment, injections are one of the most important medical tools ever invented. They allow doctors to deliver precise doses of life-saving vaccines, antibiotics, and other treatments that wouldn't work as well if swallowed.

Outside of medicine, injection means forcing any liquid into something. Engineers might talk about fuel injection in a car engine, where gasoline is sprayed into the cylinders. A factory might use injection molding to create plastic toys by forcing melted plastic into molds. Writers sometimes criticize someone for injecting their personal opinions into a supposedly neutral discussion, meaning they've pushed their views where they don't belong.

The key idea in all these uses is the same: a liquid is being forced under pressure into a space where it wouldn't naturally flow on its own.