One idea, many names

Injection happens when input from a user gets treated as an instruction rather than as data. Every injection vulnerability is that sentence, applied to a different language.

Into a database query it is SQL injection. Into a web page it is cross-site scripting. Into a system command it is command injection. Same mistake, different destination.

What you meant

Treat this as a search term
Show this comment as text
Use this as a filename

What the computer did

Ran it as part of the query
Executed it as a script
Followed it out of the folder

Every injection bug is one sentence: data was treated as instructions.

Injection is a computer mistaking data for instructions.