What are prompt templates with variables, and why are they important in production?

A prompt template is a fixed, versioned prompt skeleton with placeholder variables filled at runtime, e.g. "Summarize {document} for a {audience} in {word_count} words." It separates stable instructions from per-request data, so you write and test the wording once and reuse it consistently across calls. In production this matters for maintainability (change one template, not scattered strings), versioning and A/B testing, evaluation (compare template versions on a fixed test set), and safety (variables should be escaped or delimited so user input can't override instructions). Templating tools also help manage few-shot examples and conditional sections. Key risks: naive string interpolation enables prompt injection, and unvalidated variables can produce malformed prompts, so treat interpolation like untrusted input.