"Killer" typically refers to a person or entity that causes the death of another being, often through violent means. This term can apply to various contexts, including criminal law, where a killer may be prosecuted for murder or manslaughter. The motivations behind killing can vary widely, from personal disputes to larger societal issues. In popular culture, the term "killer" is often used in movies, books, and music to describe antagonistic characters or themes. It can also refer to fictional characters, such as serial killers in horror films, or be used metaphorically to describe something that is exceptionally good, like a "killer app" in technology.