What is the difference between a design pattern and an anti-pattern?

A design pattern is a proven solution template for a recurring design question; an anti-pattern is a pattern that is unsuitable, harmful or useless, in plain words "a bad idea".

* Same question, two answers: one proven, one that only looks clever until someone finds the hidden door. *

Both terms are used in software development and in architecture. Knowing the patterns lets an architect reuse solutions that have already worked; knowing the anti-patterns is just as valuable, because many insecure designs are familiar mistakes repeated. Security-by-obscurity, relying on attackers not knowing how something works, is a classic anti-pattern when it is the only protection.

Go deeper:

• Refactoring.Guru — What is a design pattern? — a pattern as a blueprint rather than copyable code.
• Martin Fowler — AntiPattern — the sharper original sense: something that seems like a good idea at first but leads into trouble.
• Security through obscurity — Wikipedia — why NIST says system security should not depend on the secrecy of its implementation.