To introduce a substance into a body or system using a syringe or similar device. The nurse will inject the vaccine into your arm.
To introduce or add something new or different into a situation or process. The manager decided to inject some fresh ideas into the project to boost creativity.
To forcefully introduce or insert something into a space or environment. The engineer injected steam into the chamber to increase the pressure.
Computing: To insert code or data into a computer program, system, or network, typically in order to alter its behavior. Hackers managed to inject malicious code into the database.